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Abstract:

A content management server comprises: a first connection detection unit
that detects whether or not the content management server is connected
with the content-using device; a content management unit that manages the
content according to a result of the detection by the first connection
detection unit and holds information on how the content-using device
controls the use of the content. A content-using device comprises: a
second connection detection unit that detects whether or not the
content-using device is connected with the content management server; a
second selection unit that specifies a method for controlling the use of
the content according to a result of the detection by the second
connection detection unit; and a content control unit that controls the
use of the content according to the method specified by the second
selection unit.

Claims:

1. A content distribution system including: a content management server
that manages a content; and a content-using device that uses the content,
wherein the content management server comprises: a first connection
detection unit that detects whether or not the content management server
is connected with the content-using device; a content management unit
that manages the content according to a result of the detection by the
first connection detection unit and holds information on how the
content-using device controls the use of the content, and the
content-using device comprises: a second connection detection unit that
detects whether or not the content-using device is connected with the
content management server; a second selection unit that specifies a
method for controlling the use of the content according to a result of
the detection by the second connection detection unit; and a content
control unit that controls the use of the content according to the method
specified by the second selection unit.

2. The content distribution system of claim 1, wherein when the second
connection detection unit detects that the content-using device has
transitioned from being connected with the content management server to
being unconnected with the content management server, the second
selection unit specifies, as the method for controlling the use of the
content, a method according to a period of validity of the content, and
the content control unit sets a specific period of validity with respect
to the content and, when the specific period of validity of the content
expires, stops or denies the use of the content, and when the first
connection detection unit detects that the content management server has
transitioned from being connected with the content-using device to being
unconnected with the content-using device, the content management unit
manages the content by using the method according to a period of validity
of the content and sets a specific period of validity with respect to the
content.

3. The content distribution system of claim 1, wherein when the second
connection detection unit detects that the content-using device has
transitioned from being unconnected with the content management server to
being connected with the content management server, the second selection
unit specifies, as the method for controlling the use of the content, a
method independent of a period of validity of the content, and the
content control unit cancels a specific period of validity set with
respect to the content, and when the first connection detection unit
detects that the content management server has transitioned from being
connected with the content-using device to being unconnected with the
content-using device, the content management unit manages the content by
using the method independent of a period of validity of the content, and
cancels a specific period of validity set with respect to the content.

4. The content distribution system of claim 1, wherein when the second
connection detection unit continuously detects that the content-using
device is connected with the content management server, the second
selection unit continuously specifies, as the method for controlling the
use of the content, a method according to a period of validity of the
content, and the content control unit performs updating of extending a
specific period of validity set with respect to the content, and when the
first connection detection unit continuously detects that the content
management server is connected with the content-using device, the content
management unit continuously manages the content by using the method
according to a period of validity of the content and performs updating of
extending a specific period of validity set with respect to the content.

5. The content distribution system of claim 1, wherein the content
management server further comprises: an invalidation reception unit that
receives an invalidation instruction for invalidation of the content; an
invalidation instruction transmission unit that transmits the
invalidation instruction to the content-using device; and an invalidation
response reception unit that receives, from the content-using device, an
invalidation response as a response to the invalidation instruction, the
content-using device further comprises: an invalidation instruction
reception unit that receives the invalidation instruction from the
content management server when the content-using device is connected with
the content management server; an invalidation unit that invalidates the
content according to the invalidation instruction; and an invalidation
response transmission unit that generates an invalidation response when
the content has been invalidated and transmits the invalidation response
to the content management server, the second selection unit specifies, as
the method for controlling the use of the content, a method according to
a period of validity of the content when the content-using device is
unconnected with the content management server, the content control unit
sets a specific period of validity with respect to the content, and the
invalidation unit invalidates the content when the specific period of
validity of the content expires.

6. The content distribution system of claim 1, wherein the content-using
device further comprises a content deletion unit that deletes the
content, the content control unit further records information indicating
deletion of the content when the content deletion unit has deleted the
content, the content-using device further comprises a notification unit
that, (i) when the content-using device is connected with the content
management server and the content deletion unit has deleted the content,
immediately notifies the content management server of the deletion of the
content and (ii) when the content-using device is unconnected with the
content management server and the content deletion unit has deleted the
content, notifies the content management server of the deletion of the
content after the content-using device is connected with the content
management server, and the content management unit further records
information indicating the deletion of the content.

7. A content management server managing a content and providing the
content to a content-using device, comprising: a first connection
detection unit that detects whether or not the content management server
is connected with the content-using device; and a content management unit
that manages the content according to a result of the detection by the
first connection detection unit and holds information on how the
content-using device controls the use of the content.

8. The content management server of claim 7, wherein when the first
connection detection unit detects that the content management server has
transitioned from being connected with the content-using device to being
unconnected with the content-using device, the content management unit
manages the content by using a method according to a period of validity
of the content and sets a specific period of validity with respect to the
content.

9. The content management server of claim 7, wherein when the first
connection detection unit detects that the content management server has
transitioned from being unconnected with the content-using device to
being connected with the content-using device, the content management
unit manages the content by using a method independent of a period of
validity of the content, and cancels a specific period of validity set
with respect to the content.

10. The content management server of claim 7, wherein when the first
connection detection unit continuously detects that the content
management server is connected with the content-using device, the content
management unit continuously manages the content by using a method
according to a period of validity of the content and performs updating of
extending a specific period of validity set with respect to the content.

11. The content management server of claim 7, wherein the first
connection detection unit performs polling with respect to the
content-using device at a predetermining timing, detects that the content
management server is connected with the content-using device when
receiving a polling response from the content-using device in response to
the polling, and detects that the content management server is
unconnected with the content-using device when the polling response is
not received from the content-using device within a predetermined
interval.

12. The content management server of claim 11, wherein the first
connection detection unit determines the predetermined timing according
to a period of validity of the content.

13. The content management server of claim 7, wherein the first
connection detection unit, when receiving a polling signal from the
content-using device at a predetermined timing, detects that the content
management server is connected with the content-using device, and
transmits a polling response to the content-using device.

14. The content management server of claim 7, wherein the first
connection detection unit detects that the content management server is
connected with the content-using device when receiving a notification
from the content-using device that the content-using device is connected
with the content management server.

15. The content management server of claim 7 further comprising: an
invalidation reception unit that receives an invalidation instruction for
invalidation of the content; an invalidation instruction transmission
unit that transmits the invalidation instruction to the content-using
device; and an invalidation response reception unit that receives, from
the content-using device, an invalidation response as a response to the
invalidation instruction.

16. The content management server of claim 15 further comprising a
display unit that displays a status of the invalidation of the content
performed in accordance with the invalidation instruction by referring to
the invalidation response received from the content-using device, wherein
the display unit, (i) displays invalidation completion information
indicating that the invalidation of the content has been completed by the
content-using device, when connected with the content management server,
and, (ii) displays a period of validity of the content set in the
content-using device, when unconnected with the content management
server.

17. The content management server of claim 7 further comprising a display
unit that displays how the management of the content is being performed.

18. A content-using device that uses a content provided from a content
management server managing the content, comprising: a second connection
detection unit that detects whether or not the content-using device is
connected with the content management server; a second selection unit
that specifies a method for controlling the use of the content according
to a result of the detection by the second connection detection unit; and
a content control unit that controls the use of the content according to
the method specified by the second selection unit.

19. The content-using device of claim 18, wherein when the second
connection detection unit detects that the content-using device has
transitioned from being connected with the content management server to
being unconnected with the content management server, the second
selection unit specifies, as the method for controlling the use of the
content, a method according to a period of validity of the content, and
the content control unit sets a specific period of validity with respect
to the content and, when the specific period of validity of the content
expires, stops or denies the use of the content.

20. The content-using device of claim 18, wherein when the second
connection detection unit detects that the content-using device has
transitioned from being unconnected with the content management server to
being connected with the content management server, the second selection
unit specifies, as the method for controlling the use of the content, a
method independent of a period of validity of the content, and the
content control unit cancels a specific period of validity set with
respect to the content.

21. The content-using device of claim 18, wherein when the second
connection detection unit continuously detects that the content-using
device is connected with the content management server, the second
selection unit continuously specifies, as the method for controlling the
use of the content, a method according to a period of validity of the
content, and the content control unit performs updating of extending a
specific period of validity set with respect to the content.

22. The content-using device of claim 18, wherein the second connection
detection unit detects whether or not the content-using device is
connected with the content management server by performing either one of
or any combination of: (i) detecting, at a predetermined timing, whether
or not a polling signal is received from the content management server at
the predetermining timing; (ii) detecting whether or not a communication
module provided to the content-using device is activated; (iii) detecting
whether or not the content-using device is located within a distance,
from an access point, within which radio signals from the content-using
device reach the access point; and (iv) detecting whether a user
operation is performed with respect to the content-using device for
activating or deactivating communication by the content-using device.

23. The content-using device of claim 18, wherein the second connection
detection unit, when detecting that the content-using device is connected
with the content management server, performs polling with respect to the
content management server and receives a polling response from the
content management server as a response to the polling, and the content
control unit, when the polling response permits extension of a period of
validity set with respect to the content, performs updating of extending
the period of validity.

24. The content-using device of claim 23, wherein the second connection
detection unit determines a timing at which the polling is performed
according to the period of validity.

25. The content-using device of claim 18, wherein the second connection
detection unit, when detecting that the content-using device is connected
with the content management server, transmits a notification to the
content management server that the content-using device is connected with
the content management server, and the second connection detection unit
detects whether or not the content-using device is connected with the
content management server by performing either one of or any combination
of: (i) detecting, at a predetermined timing, whether or not a polling
signal is received from the content management server at the
predetermining timing; (ii) detecting whether or not a communication
module provided to the content-using device is activated; (iii) detecting
whether or not the content-using device is located within a distance,
from an access point, within which radio signals from the content-using
device reach the access point; and (iv) detecting whether a user
operation is performed with respect to the content-using device for
activating or deactivating communication by the content-using device.

26. The content-using device of claim 18 further comprising: an
invalidation instruction reception unit that receives an invalidation
instruction from the content management server when the content-using
device is connected with the content management server; an invalidation
unit that invalidates the content according to the invalidation
instruction; and an invalidation response transmission unit that
generates an invalidation response when the content has been invalidated
and transmits the invalidation response to the content management server.

27. The content-using device of claim 26 further comprising: a display
unit that displays a record of the invalidation of the content performed
according to the invalidation instruction when the invalidation unit has
invalidated the content.

28. The content-using device of claim 18 further comprising a display
unit that displays how the control of the use of the content is being
performed by the content control unit.

29. The content-using device of claim 18 further comprising: an
invalidation instruction reception unit that receives an invalidation
instruction from the content management server when the content-using
device is connected with the content management server; an invalidation
unit that invalidates the content according to the invalidation
instruction; an invalidation response transmission unit that generates an
invalidation response when the content has been invalidated and transmits
the invalidation response to the content management server, wherein the
second selection unit specifies, as the method for controlling the use of
the content, a method according to a period of validity of the content
when the content-using device is unconnected with the content management
server, the content control unit sets a specific period of validity with
respect to the content, and the invalidation unit invalidates the content
when the specific period of validity of the content expires.

30. The content-using device of claim 18 further comprising a content
deletion unit that deletes the content, wherein the content control unit
further records information indicating deletion of the content when the
content deletion unit has deleted the content, the content-using device
further comprises: a notification unit that, (i) when the content-using
device is connected with the content management server and the content
deletion unit has deleted the content, immediately notifies the content
management server of the deletion of the content and, (ii) when the
content-using device is unconnected with the content management server
and the content deletion unit has deleted the content, notifies the
content management server of the deletion of the content after the
content-using device is connected with the content management server.

31. A control method used in a content distribution system including: a
content management server that manages a content; and a content-using
device that uses the content, comprising: a first connection detection
step, by the content management server, of detecting whether or not the
content management server is connected with the content-using device; a
content management step, by the content management server, of managing
the content according to a result of the detection in the first
connection detection step and of holding information on how the
content-using device controls the use of the content; a second connection
detection step, by the content-using device, of detecting whether or not
the content-using device is connected with the content management server;
a second selection step, by the content-using device, of specifying a
method for controlling the use of the content according to a result of
the detection in the second connection detection step; and a content
control step, by the content-using device, of controlling the use of the
content according to the method specified in the second selection step.

32. An integrated circuit that forms a content management server managing
a content and providing the content to a content-using device,
comprising: a first connection detection unit that detects whether or not
the content management server is connected with the content-using device;
and a content management unit that manages the content according to a
result of the detection by the first connection detection unit and holds
information on how the content-using device controls the use of the
content.

33. An integrated circuit that forms a content-using device that uses a
content provided from a content management server managing the content,
comprising: a second connection detection unit that detects whether or
not the content-using device is connected with the content management
server; a second selection unit that specifies a method for controlling
the use of the content according to a result of the detection by the
second connection detection unit; and a content control unit that
controls the use of the content according to the method specified by the
second selection unit.

Description:

TECHNICAL FIELD

[0001] The present invention relates to a technology related to management
of a content distributed via a network.

BACKGROUND ART

[0002] In recent years, business utilizing personal contents, such as the
exchange of photos and video contents over Social Networking Service
(SNS) websites, has been becoming more and more popular. In addition, as
development of infrastructure supporting such exchange of personal
contents progresses, opportunities are increasing where people belonging
to a same group exchange with each other personal contents, such as
photos taken at a travel destination and video contents taken at a school
sports festival or a school play.

[0003] For instance, Patent Literature 1 discloses a technology as
described in the following. A content management server checks, via a
network, whether or not a content-using device is connected with the
content management server. When the content-using device is connected
with the content management server, the content management server
transmits, via the network, a copy deletion command to the content-using
device. The content deletion command includes a content ID corresponding
to an invalidation-target content. The content-using device receives the
copy deletion command from the content management server and executes
deletion processing with respect to a copied content corresponding to the
content ID included in the copy deletion command. In contrast, when the
content-using device is not connected with the content management server,
the content management server repeatedly tries to establish a connection
with the content-using device until the deletion processing with respect
to the copied content is completed. As such, the technology disclosed in
Patent Literature 1 prevents the use of an unauthorized copied content.

CITATION LIST

Patent Literature

[Patent Literature 1]

[0004] Japanese Patent Publication No. 4186886

[Patent Literature 2]

[0004]

[0005] Japanese Patent Publication No. 4463320

[Patent Literature 3]

[0005]

[0006] Japanese Patent Application Publication No. 2005-250881

[Patent Literature 4]

[0006]

[0007] Japanese Patent Application Publication No. 2011-138209

SUMMARY OF INVENTION

Technical Problem

[0008] However, according to the technology disclosed in Patent Literature
1, the content-using device cannot receive the copy deletion command from
the content management server when the content-using device is not
connected with the content management server. This gives rise to a
situation where, although the content management server is instructing
the content-using device to delete the copied content, the content-using
device cannot actually delete the copied content. In such a case, a user
of the content-using device, which is not connected with the content
management server, is able to use the copied content while protection is
not realized of an original content having been provided by a provider.
As such, when employing the technology disclosed in Patent Literature 1,
there is an imbalance between the use of a given content by a user and
the right of a provider having provided the content.

[0009] In view of such a problem, the present invention provides a content
distribution server, a content management server, a content-using device,
and a control method according to which, regardless of whether or not a
content-using device is connected with a content management server,
protection of a content provided by a provider is secured while a user
utilizing the content is able to use the content with an enhanced degree
of convenience.

Solution to Problem

[0010] One aspect of the present invention is a content distribution
system including: a content management server that manages a content; and
a content-using device that uses the content, wherein the content
management server comprises: a first connection detection unit that
detects whether or not the content management server is connected with
the content-using device; a content management unit that manages the
content according to a result of the detection by the first connection
detection unit and holds information on how the content-using device
controls the use of the content, and the content-using device comprises:
a second connection detection unit that detects whether or not the
content-using device is connected with the content management server; a
second selection unit that specifies a method for controlling the use of
the content according to a result of the detection by the second
connection detection unit; and a content control unit that controls the
use of the content according to the method specified by the second
selection unit.

Advantageous Effects of the Invention

[0011] According to the content distribution system pertaining to one
aspect of the present invention, the management of a content in the
content distribution system is performed according to a method for
controlling the use of the content which is determined according to
whether or not the content-using device is connected with the content
management server. As such, protection of the content, which has been
provided by a provider, is realized while a user utilizing the content is
able to use the content with an enhanced degree of convenience.

BRIEF DESCRIPTION OF DRAWINGS

[0012] FIG. 1 illustrates an overall configuration of a content
distribution system 40 in embodiment 1.

[0013]FIG. 2 illustrates an overall configuration of a content
distribution system 10 in embodiment 2, including a configuration of a
content management server 100 and a configuration of a content-using
device 200.

[0022] FIG. 11 illustrates a configuration of a content control unit 202.

[0023]FIG. 12 is a chart indicating one example of a data configuration
of a content management list 222.

[0024]FIG. 13 is a chart indicating one example of a data configuration
of a content management list 222a.

[0025]FIG. 14 is the first part of a sequence diagram illustrating
operations of the content distribution system 10, a following part of
which illustrated in FIG. 15.

[0026] FIG. 15 is the second part of the sequence diagram illustrating the
operations of the content distribution system 10, a following part of
which illustrated in FIG. 16.

[0027] FIG. 16 is the third part of the sequence diagram illustrating the
operations of the content distribution system 10.

[0028] FIG. 17 is the first part of a sequence diagram illustrating
operations of the content-using device 200.

[0029] FIG. 18 is the fourth part of the sequence diagram illustrating the
operations of the content distribution system 10, a following part of
which illustrated in FIG. 19.

[0030] FIG. 19 is the fifth part of the sequence diagram illustrating the
operations of the content distribution system 10.

[0031] FIG. 20 is the second part of the sequence diagram illustrating the
operations of the content-using device 200.

[0032] FIG. 21 illustrates a configuration of a content distribution
system 10a.

[0033]FIG. 22 is a sequence diagram illustrating interaction between a
content management server 100a and a content-using device 200a in a case
where the content-using device 200a transitions from online to offline
during the interaction.

[0034]FIG. 23 is a sequence diagram illustrating interaction between the
content management server 100a and the content-using device 200a in a
case where, during the interaction, the content-using device 200a first
transitions from online to offline and then returns to online once again.

[0035] FIG. 24 illustrates an overall configuration of a content
distribution system 20 in embodiment 2, including a configuration of a
content management server 400 and a configuration of a content-using
device 500.

[0044]FIG. 33 is the first part of a sequence diagram illustrating
operations of the content distribution system 20.

[0045] FIG. 34 is the second part of the sequence diagram illustrating the
operations of the content distribution system 20.

[0046]FIG. 35 illustrates operations in a case where, among contents held
by one content-using device that is online, invalidation is performed of
all contents having been provided from one content management server.

[0047]FIG. 36 illustrates operations in a case where, among contents held
by one content-using device that is offline, invalidation is performed of
all contents having been provided from one content management server.

[0048]FIG. 37 illustrates operations in a case where invalidation of one
content is performed with respect to multiple content-using devices that
are online.

[0049]FIG. 38 illustrates operations in a case where invalidation of one
content is performed with respect to multiple content-using devices, some
of which being offline and the others being online.

[0050]FIG. 39 illustrates an overall configuration of a content
distribution system 30 in embodiment 4, including a configuration of a
content management server 600 and a configuration of a content-using
device 700.

[0059]FIG. 48 illustrates a configuration of a content control unit 702.

[0060]FIG. 49 is a chart indicating one example of a data configuration
of a content management list 722.

[0061]FIG. 50 is a chart indicating one example of a data configuration
of a content management list 722a.

[0062]FIG. 51 is a flowchart illustrating operations involved in updating
of the content management list 631 by a content management control unit
630.

[0063] FIG. 52 is a sequence diagram illustrating operations of the
content-using device 600 when receiving a polling command from the
content-using device 700.

[0064]FIG. 53 is the first part of a sequence diagram illustrating
operations of the content-using device 700 when outputting a polling
command, a following part of which illustrated in FIG. 54.

[0065]FIG. 54 is the second part of the sequence diagram illustrating the
operations of the content-using device 700 when outputting the polling
command.

[0066]FIG. 55 is a sequence diagram illustrating operations of the
content-using device 700 when determining how a content is to be used.

[0067]FIG. 56 illustrates a configuration of a content distribution
system 30a.

[0068]FIG. 57 is the first part of a sequence diagram illustrating
interaction between a content management server 600a and a content-using
device 700a, a following part of which illustrated in FIG. 58.

[0069]FIG. 58 is the second part of the sequence diagram illustrating the
interaction between the content management server 600a and the
content-using device 700a.

[0070]FIG. 59 is a chart indicating one example of a data configuration
of a content management list 631b.

[0071]FIG. 60 is a chart indicating one example of a data configuration
of a content management list 722b.

[0072] FIG. 61 illustrates one example of a data configuration of an
invalidation instruction 351.

[0073]FIG. 62 illustrates an overall configuration of a content
distribution system 50 pertaining to a modification.

[0074]FIG. 63 is a sequence diagram illustrating processing in the
content distribution system 50 where a relay server 950a transmits a
polling command to a content-using device 900a according to an
instruction from a content management server 800a.

[0075]FIG. 64 is a sequence diagram illustrating processing in the
content distribution system 50 where the relay server 950a transmits the
polling command to the content management server 800a according to an
instruction from the content-using device 900a.

[0076]FIG. 65 is a sequence diagram illustrating processing in the
content distribution system 50 where the relay server 950a transmits an
invalidation instruction to the content-using device 900a according to an
instruction from the content management server 800a.

[0077] FIG. 66 is a sequence diagram illustrating processing in the
content distribution system 50 where the relay server 950a, in response
to polling performed by the content-using device 900a, searches for an
invalidation instruction and transmits a response to the content-using
device 900a.

[0078] FIG. 67 is a sequence diagram illustrating operations of the
content-using device 200, which is offline, when performing self-deletion
of a content before a scheduled expiration time.

[0079]FIG. 68 is a sequence diagram illustrating operations of the
content-using device 200, which is online, when performing self-deletion
of a content before a scheduled expiration time.

[0080]FIG. 69 is a chart indicating one example of a data configuration
of a content management list 222b.

DESCRIPTION OF EMBODIMENTS

[0081] One aspect of the present invention is a content distribution
system including: a content management server that manages a content; and
a content-using device that uses the content, wherein the content
management server comprises: a first connection detection unit that
detects whether or not the content management server is connected with
the content-using device; a content management unit that manages the
content according to a result of the detection by the first connection
detection unit and holds information on how the content-using device
controls the use of the content, and the content-using device comprises:
a second connection detection unit that detects whether or not the
content-using device is connected with the content management server; a
second selection unit that specifies a method for controlling the use of
the content according to a result of the detection by the second
connection detection unit; and a content control unit that controls the
use of the content according to the method specified by the second
selection unit.

[0082] According to the content distribution system pertaining to one
aspect of the present invention, the management of a content in the
content distribution system is performed according to a method for
controlling the use of the content which is determined according to
whether or not the content-using device is connected with the content
management server. As such, protection of the content, which has been
provided by a provider, is realized while a user utilizing the content is
able to use the content with an enhanced degree of convenience.

[0083] In the content distribution system, when the second connection
detection unit detects that the content-using device has transitioned
from being connected with the content management server to being
unconnected with the content management server, the second selection unit
may specify, as the method for controlling the use of the content, a
method according to a period of validity of the content, and the content
control unit may set a specific period of validity with respect to the
content and, when the specific period of validity of the content expires,
may stop or deny the use of the content, and the first connection
detection unit detects that the content management server has
transitioned from being connected with the content-using device to being
unconnected with the content-using device, the content management unit
may manage the content by using the method according to a period of
validity of the content and may set a specific period of validity with
respect to the content.

[0084] According to this structure, the content-using device, when
self-detecting the transition from being connected with the content
management server to being unconnected with the content management
server, selects, as the method for controlling the use of the content,
the method according to a period of validity of the content, and further,
when the period of validity of the content expires, the content-using
device stops or denies the use of the content. This enables a user of the
content-using device to use the content during the period of validity of
the content. Further, after the period of validity of the content
expires, protection of the content having been provided by a provider is
ensured. On the other hand, the content management server, when detecting
that the content management server has transitioned from being connected
with the content-using device to being unconnected with the content-using
device, manages the content by using the method according to a period of
validity of the content and sets a period of validity with respect to the
content. This enables the content management server to manage the content
according to a period of validity of the content. As such, the provider
of the content is freed from concerns

[0085] In the content distribution system, when the second connection
detection unit detects that the content-using device has transitioned
from being unconnected with the content management server to being
connected with the content management server, the second selection unit
may specify, as the method for controlling the use of the content, a
method independent of a period of validity of the content, and the
content control unit may cancel a specific period of validity set with
respect to the content, and when the first connection detection unit
detects that the content management server has transitioned from being
connected with the content-using device to being unconnected with the
content-using device, the content management unit may manage the content
by using the method independent of a period of validity of the content,
and may cancel a specific period of validity set with respect to the
content.

[0086] According to this structure, the content-using device, when
self-detecting the transition from being unconnected with the content
management server to being connected with the content management server,
specifies, as the method for controlling the use of the content, a method
independent of a period of validity of the content, and further, cancels
the period of validity set with respect to the content. This enables a
user to use the content. On the other hand, the content management
server, when detecting that the content management server has
transitioned from being unconnected with the content-using device to
being connected with the content-using device, manages the content by
using the method independent of a period of validity of the content, and
cancels a period of validity set with respect to the content. In this
case, a provider of the content is freed from concerns since the
content-using device is connected with the content management server.

[0087] In the content distribution system, when the second connection
detection unit continuously detects that the content-using device is
connected with the content management server, the second selection unit
may continuously specify, as the method for controlling the use of the
content, a method according to a period of validity of the content, and
the content control unit may perform updating of extending a specific
period of validity set with respect to the content, and when the first
connection detection unit continuously detects that the content
management server is connected with the content-using device, the content
management unit may continuously manage the content by using the method
according to a period of validity of the content and may perform updating
of extending a specific period of validity set with respect to the
content.

[0088] According to this structure, the content-using device, when
continuously self-detecting that the content-using device is connected
with the content management server, continuously specifies, as the method
for controlling the use of the content, the method according to a period
of validity of the content, and further, performs updating of extending a
period of validity set with respect to the content. This enables a user
to continue the use of the content. On the other hand, the content
management server, when continuously detecting that the content
management server is connected with the content-using device,
continuously manages the content by using the method according to a
period of validity of the content and performs updating of extending a
period of validity set with respect to the content. In this case, the
provider of the content is freed from concerns since the content-using
device is connected with the content management server.

[0089] In the content distribution system, the content management server
may further comprise: an invalidation reception unit that receives an
invalidation instruction for invalidation of the content; an invalidation
instruction transmission unit that transmits the invalidation instruction
to the content-using device; and an invalidation response reception unit
that receives, from the content-using device, an invalidation response as
a response to the invalidation instruction, the content-using device may
further comprise: an invalidation instruction reception unit that
receives the invalidation instruction from the content management server
when the content-using device is connected with the content management
server; an invalidation unit that invalidates the content according to
the invalidation instruction; and an invalidation response transmission
unit that generates an invalidation response when the content has been
invalidated and transmits the invalidation response to the content
management server, the second selection unit may specify, as the method
for controlling the use of the content, a method according to a period of
validity of the content when the content-using device is unconnected with
the content management server, the content control unit may set a
specific period of validity with respect to the content, and the
invalidation unit may invalidate the content when the specific period of
validity of the content expires.

[0090] According to this structure, when the content-using device is
unconnected with the content management server, the content control unit
specifies, as the method for controlling the use of the content, the
method according to a period of validity of the content, sets a specific
period of validity with respect to the content, and further, invalidates
the content when the specific period of validity of the content expires.
This results in protection of the content provided by a provider being
ensured after the period of validity of the content expires.

[0091] In the content distribution system, the content-using device may
further comprise a content deletion unit that deletes the content, the
content control unit may further record information indicating deletion
of the content when the content deletion unit has deleted the content,
the content-using device may further comprise a notification unit that,
(i) when the content-using device is connected with the content
management server and the content deletion unit has deleted the content,
immediately notifies the content management server of the deletion of the
content and (ii) when the content-using device is unconnected with the
content management server and the content deletion unit has deleted the
content, notifies the content management server of the deletion of the
content after the content-using device is connected with the content
management server, and the content management unit may further record
information indicating the deletion of the content.

[0092] According to this structure, the content-using device, when
connected with the content management server, immediately notifies the
content management server that the content has been deleted. On the other
hand, the content-using device, when unconnected with the content
management server, notifies the content management server that the
content has been deleted after detecting the transition from being
unconnected with the content management server to being connected with
the content management server. This enables the content management server
to acknowledge that the content has been self-deleted by the
content-using device.

[0093] Another aspect of the present invention is a content management
server managing a content and providing the content to a content-using
device, comprising: a first connection detection unit that detects
whether or not the content management server is connected with the
content-using device; and a content management unit that manages the
content according to a result of the detection by the first connection
detection unit and holds information on how the content-using device
controls the use of the content.

[0094] According to the content management server pertaining to one aspect
of the present invention, the management of a content is performed
according to a method for controlling the use of the content which is
determined according to whether or not the content management server is
connected with the content-using device. This results in protection of
the content, which has been provided by a provider, being realized while
a user utilizing the content is able to use the content with an enhanced
degree of convenience.

[0095] In the content management server, when the first connection
detection unit detects that the content management server has
transitioned from being connected with the content-using device to being
unconnected with the content-using device, the content management unit
may manage the content by using a method according to a period of
validity of the content and may set a specific period of validity with
respect to the content.

[0096] According to this structure, the content management server, when
detecting that the content management server has transitioned from being
connected with the content-using device to being unconnected with the
content-using device, manages the content according to the method
according to a period of validity of the content and sets a specific
period of validity with respect to the content. This enables the content
management server to manage the content according to a period of validity
of the content. As such, a provider of the content is freed from
concerns.

[0097] In the content management server, when the first connection
detection unit detects that the content management server has
transitioned from being unconnected with the content-using device to
being connected with the content-using device, the content management
unit may manage the content by using a method independent of a period of
validity of the content, and may cancel the specific period of validity
set with respect to the content.

[0098] According to this structure, the content management server, when
detecting that the content management server has transitioned from being
unconnected with the content-using device to being connected with the
content-using device, manages the content by using the method independent
of a period of validity of the content, and cancels the specific period
of validity set with respect to the content in the content management
server. In this case, a provider of the content is freed from concerns
since the content-using device is connected with the content management
server.

[0099] In the content management server, when the first connection
detection unit continuously detects that the content management server is
connected with the content-using device, the content management unit may
continuously manage the content by using a method according to a period
of validity of the content and may perform updating of extending a
specific period of validity set with respect to the content.

[0100] According to this structure, the content management server, when
continuously detecting that the content management server is connected
with the content-using device, continuously manages the content by using
the method according to a period of validity of the content and performs
updating of extending a specific period of validity set with respect to
the content. In this case, a provider of the content is freed from
concerns since the content-using device is connected with the content
management server.

[0101] In the content management server, the first connection detection
unit may perform polling with respect to the content-using device at a
predetermining timing, may detect that the content management server is
connected with the content-using device when receiving a polling response
from the content-using device in response to the polling, and may detect
that the content management server is unconnected with the content-using
device when the polling response is not received from the content-using
device within a predetermined interval.

[0102] According to this structure, the content management server detects
whether or not the content management server is connected with the
content-using device according to reception or non-reception of a polling
response from the content-using device.

[0103] In the content management server, the first connection detection
unit may determine the predetermined timing according to a period of
validity of the content.

[0104] According to this structure, the content management server
determines the predetermined timing at which polling is performed with
respect to the content-using device according to a period of validity of
the content. This enables effectively determining the timing at which
polling is performed.

[0105] In the content management server, the first connection detection
unit, when receiving a polling signal from the content-using device at a
predetermined timing, may detect that that the content management server
is connected with the content-using device, and may transmit a polling
response to the content-using device.

[0106] According to this structure, the content management server detects
whether or not the content management server is connected with the
content-using device according to polling performed by the content-using
device with respect to the content management server. As such, the
content management server need not check whether or not a connection is
established between the content management server and the content-using
device.

[0107] In the content management server, the first connection detection
unit may detect that the content management server is connected with the
content-using device when receiving a notification from the content-using
device that the content-using device is connected with the content
management server.

[0108] According to this structure, the content management server detects
that the content management server is connected with the content-using
device when receiving a notification from the content-using device that
the content-using device is connected with the content management server.
As such, the content management server need not check whether or not a
connection is established between the content management server and the
content-using device.

[0109] The content management server may further comprise: an invalidation
reception unit that receives an invalidation instruction for invalidation
of the content; an invalidation instruction transmission unit that
transmits the invalidation instruction to the content-using device; and
an invalidation response reception unit that receives, from the
content-using device, an invalidation response as a response to the
invalidation instruction.

[0110] According to this structure, the content management server
transmits an invalidation instruction for invalidation of a content to
the content-using device and receives, from the content-using device, an
invalidation response as a response to the invalidation instruction. As
such, the content management server causes the content-using device to
perform invalidation of the content.

[0111] The content management server may further comprise a display unit
that displays a status of the invalidation of the content performed in
accordance with the invalidation instruction by referring to the
invalidation response received from the content-using device, wherein the
display unit, (i) may display invalidation completion information
indicating that the invalidation of the content has been completed by the
content-using device, when connected with the content management server,
and, (ii) may display a period of validity of the content set in the
content-using device, when unconnected with the content management
server.

[0112] According to this structure, the content management server displays
invalidation completion information indicating that the invalidation of
the content has been completed by the content-using device, when
connected with the content management server. Further, the content
management server displays a period of validity of the content set in the
content-using device, when unconnected with the content management
server. As such, a provider of the content is acknowledged of the status
of the invalidation of the content.

[0113] The content management server may further comprise a display unit
that displays how the management of the content is being performed.

[0114] According to this structure, the content management server displays
how the management of the content is being performed. As such, a provider
of the content is acknowledged of how the management of the content is
being performed.

[0115] Another aspect of the present invention is a content-using device
that uses a content provided from a content management server managing
the content, comprising: a second connection detection unit that detects
whether or not the content-using device is connected with the content
management server; a second selection unit that specifies a method for
controlling the use of the content according to a result of the detection
by the second connection detection unit; and a content control unit that
controls the use of the content according to the method specified by the
second selection unit.

[0116] According to the content-using device pertaining to one aspect of
the present invention, the management of a content is performed according
to a method for controlling the use of the content which is determined
according to whether or not the content-using device is connected with
the content management server. This results in protection of the content,
which has been provided by a provider, being realized while a user
utilizing the content is able to use the content with an enhanced degree
of convenience.

[0117] In the content-using device, when the second connection detection
unit detects that the content-using device has transitioned from being
connected with the content management server to being unconnected with
the content management server, the second selection unit may specify, as
the method for controlling the use of the content, a method according to
a period of validity of the content, and the content control unit may set
a specific period of validity with respect to the content and, when the
specific period of validity of the content expires, may stop or deny the
use of the content.

[0118] According to this structure, the content-using device, when
self-detecting the transition from being connected with the content
management server to being unconnected with the content management
server, selects, as the method for controlling the use of the content,
the method according to a period of validity of the content. Further,
when the period of validity of the content expires, the content-using
device stops or denies the use of the content. This enables a user of the
content-using device to use the content during the period of validity of
the content. Further, after the period of validity of the content
expires, protection of the content having been provided by a provider is
ensured.

[0119] In the content-using device, when the second connection detection
unit detects that the content-using device has transitioned from being
unconnected with the content management server to being connected with
the content management server, the second selection unit may specify, as
the method for controlling the use of the content, a method independent
of a period of validity of the content, and the content control unit may
cancel a specific period of validity set with respect to the content.

[0120] According to this structure, the content-using device, when
self-detecting the transition from being unconnected with the content
management server to being connected with the content management server,
specifies, as the method for controlling the use of the content, a method
independent of a period of validity of the content, and further, cancels
the period of validity set with respect to the content. This enables a
user to use the content.

[0121] In the content-using device, when the second connection detection
unit continuously detects that the content-using device is connected with
the content management server, the second selection unit may continuously
specify, as the method for controlling the use of the content, a method
according to a period of validity of the content, and the content control
unit may perform updating of extending a specific period of validity set
with respect to the content.

[0122] According to this structure, the content-using device, when
continuously self-detecting that the content-using device is connected
with the content management server, continuously specifies, as the method
for controlling the use of the content, the method according to a period
of validity of the content, and further, performs updating of extending a
period of validity set with respect to the content. As such, a user is
able to continue the use of the content.

[0123] In the content-using device, the second connection detection unit
may detect whether or not the content-using device is connected with the
content management server by performing either one of or any combination
of: (i) detecting, at a predetermined timing, whether or not a polling
signal is received from the content management server at the
predetermining timing; (ii) detecting whether or not a communication
module provided to the content-using device is activated; (iii) detecting
whether or not the content-using device is located within a distance,
from an access point, within which radio signals from the content-using
device reach the access point; and (iv) detecting whether a user
operation is performed with respect to the content-using device for
activating or deactivating communication by the content-using device.

[0124] According to this structure, the content-using device detects
whether or not the content-using device is connected with the content
management server in various ways including detecting polling, detecting
whether or not a communication module is activated, detecting whether or
not the content-using device is located within a distance within which
radios signals are reachable, and detecting a user operation performed
with respect to the content-using device for activating/deactivating
communication.

[0125] In the content-using device, the second connection detection unit,
when detecting that the content-using device is connected with the
content management server, may perform polling with respect to the
content management server and may receive a polling response from the
content management server as a response to the polling, and the content
control unit, when the polling response permits extension of a period of
validity set with respect to the content, may perform updating of
extending the period of validity.

[0126] According to this structure, the content-using device performs
polling with respect to the content management server, and when a polling
response received as a response to the polling permits extension of a
period of validity set with respect to the content, performs updating of
extending the period of validity set with respect to the content. As
such, a user of the content-using device is able to continue the use of
the content.

[0127] In the content-using device, the second connection detection unit
may determine a timing at which the polling is performed according to the
period of validity.

[0128] According to this structure, the content-using device determines
the predetermined timing at which polling is performed with respect to
the content management server according to a period of validity of the
content set in the content-using device. This enables effectively
determining the timing at which polling is performed.

[0129] In the content-using device, the second connection detection unit,
when detecting that the content-using device is connected with the
content management server, may transmit a notification to the content
management server that the content-using device is connected with the
content management server, and the second connection detection unit may
detect whether or not the content-using device is connected with the
content management server by performing either one of or any combination
of: (i) detecting, at a predetermined timing, whether or not a polling
signal is received from the content management server at the
predetermining timing; (ii) detecting whether or not a communication
module provided to the content-using device is activated; (iii) detecting
whether or not the content-using device is located within a distance,
from an access point, within which radio signals from the content-using
device reach the access point; and (iv) detecting whether a user
operation is performed with respect to the content-using device for
activating or deactivating communication by the content-using device.

[0130] According to this structure, the content-using device detects
whether or not the content-using device is connected with the content
management server in various ways including the detection of polling,
detecting whether or not a communication module is activated, detecting
whether or not the content-using device is located within a distance
within which radios signals are reachable, and detecting a user operation
performed with respect to the content-using device for
activating/deactivating communication, and, when detecting that the
content-using device is connected with the content management server,
transmits a notification to the content management server that the
content-using device is connected with the content management server.

[0131] The content-using device may further comprise: an invalidation
instruction reception unit that receives an invalidation instruction from
the content management server when the content-using device is connected
with the content management server; an invalidation unit that invalidates
the content according to the invalidation instruction; and an
invalidation response transmission unit that generates an invalidation
response when the content has been invalidated and transmits the
invalidation response to the content management server.

[0132] According to this structure, the content-using device receives an
invalidation instruction for invalidation of the content from the content
management server and invalidates the content. This results in protection
of the content being ensured.

[0133] The content-using device may further comprise: a display unit that
displays a record of the invalidation of the content performed according
to the invalidation instruction when the invalidation unit has
invalidated the content.

[0134] According to this structure, the content-using device displays a
record of the invalidation of the content when the invalidation unit has
invalidated the content. As such, a user is acknowledged of a record of
the invalidation of the content.

[0135] The content-using device may further comprise a display unit that
displays how the control of the use of the content is being performed by
the content control unit.

[0136] According to this structure, the content-using device displays how
the control of the use of the content is being performed by the content
control unit. As such, a user is acknowledged of how the control is being
performed.

[0137] The content-using device may further comprise: an invalidation
instruction reception unit that receives an invalidation instruction from
the content management server when the content-using device is connected
with the content management server; an invalidation unit that invalidates
the content according to the invalidation instruction; an invalidation
response transmission unit that generates an invalidation response when
the content has been invalidated and transmits the invalidation response
to the content management server, wherein the second selection unit may
specify, as the method for controlling the use of the content, a method
according to a period of validity of the content when the content-using
device is unconnected with the content management server, the content
control unit may set a specific period of validity with respect to the
content, and the invalidation unit may invalidate the content when the
specific period of validity of the content expires.

[0138] According to this structure, when the content-using device is
unconnected with the content management server, the content control unit
specifies, as the method for controlling the use of the content, the
method according to a period of validity of the content, sets a specific
period of validity with respect to the content, and further, invalidates
the content when the specific period of validity of the content expires.
This results in protection of the content provided by a provider being
ensured after the period of validity of the content expires.

[0139] The content-using device may further comprise a content deletion
unit that deletes the content, wherein the content control unit may
further record information indicating deletion of the content when the
content deletion unit has deleted the content, the content-using device
may further comprise: a notification unit that, (i) when the
content-using device is connected with the content management server and
the content deletion unit has deleted the content, immediately notifies
the content management server of the deletion of the content and, (ii)
when the content-using device is unconnected with the content management
server and the content deletion unit has deleted the content, notifies
the content management server of the deletion of the content after the
content-using device is connected with the content management server.

[0140] According to this structure, the content-using device, when
connected with the content management server, immediately notifies the
content management server that the content has been deleted. On the other
hand, the content-using device, when unconnected with the content
management server, notifies the content management server that the
content has been deleted after detecting the transition from being
unconnected with the content management server to being connected with
the content management server. As such, the content management server is
able to acknowledge that the content has been self-deleted by the
content-using device.

[0141] Another aspect of the present invention is a control method used in
a content distribution system including: a content management server that
manages a content; and a content-using device that uses the content,
comprising: a first connection detection step, by the content management
server, of detecting whether or not the content management server is
connected with the content-using device; a content management step, by
the content management server, of managing the content according to a
result of the detection in the first connection detection step and of
holding information on how the content-using device controls the use of
the content; a second connection detection step, by the content-using
device, of detecting whether or not the content-using device is connected
with the content management server; a second selection step, by the
content-using device, of specifying a method for controlling the use of
the content according to a result of the detection in the second
connection detection step; and a content control step, by the
content-using device, of controlling the use of the content according to
the method specified in the second selection step.

[0142] According to the control method pertaining to one aspect of the
present invention, the management of a content in the content
distribution system is performed according to a method for controlling
the use of the content which is determined according to whether or not
the content-using device is connected with the content management server.
This results in protection of the content, which has been provided by a
provider, being realized while a user utilizing the content is able to
use the content with an enhanced degree of convenience.

[0143] Another aspect of the present invention is an integrated circuit
that forms a content management server managing a content and providing
the content to a content-using device, comprising: a first connection
detection unit that detects whether or not the content management server
is connected with the content-using device; and a content management unit
that manages the content according to a result of the detection by the
first connection detection unit and holds information on how the
content-using device controls the use of the content.

[0144] According to the integrated circuit pertaining to one aspect of the
present invention, the management of a content is performed according to
a method for controlling the use of the content which is determined
according to whether or not the content management server is connected
with the content-using device. This results in protection of the content,
which has been provided by a provider, being realized while a user
utilizing the content is able to use the content with an enhanced degree
of convenience.

[0145] Another aspect of the present invention is an integrated circuit
that forms a content-using device that uses a content provided from a
content management server managing the content, comprising: a second
connection detection unit that detects whether or not the content-using
device is connected with the content management server; a second
selection unit that specifies a method for controlling the use of the
content according to a result of the detection by the second connection
detection unit; and a content control unit that controls the use of the
content according to the method specified by the second selection unit.

[0146] According to the integrated circuit pertaining to one aspect of the
present invention, the management of a content is performed according to
a method for controlling the use of the content which is determined
according to whether or not the content-using device is connected with
the content management server. This results in, protection of the
content, which has been provided by a provider, being realized while a
user utilizing the content is able to use the content with an enhanced
degree of convenience.

1. Embodiment 1

[0147] In the following, description is provided on a content distribution
system 40 pertaining to embodiment 1 of the present invention, with
reference to the accompanying drawings.

[0148] (1) Configuration of Content Distribution System 40

[0149] FIG. 1 illustrates an overall configuration of the content
distribution system 40. The content distribution system 40 includes a
content management server 800 and a content-using device 900.

[0151] The content management server 800 comprises: a first connection
detection unit 802; and a content management unit 801. The first
connection detection unit 802 detects whether or not the content
management server 800 is connected with the content-using device 900. The
content management unit 801 manages the content according to a result of
the detection by the first connection detection unit 802. The content
management unit 801 holds information on how the content-using device 900
controls the use of the content.

[0152] The content-using device 900 comprises: a second connection
detection unit 901; a second selection unit 903; and a content control
unit 902. The second connection detection unit 901 detects whether or not
the content-using device 900 is connected with the content management
server 800. The second selection unit 903 specifies a method for
controlling the use of the content according to a result of the detection
by the second connection detection unit 901. The content control unit 902
controls the use of the content according to the method specified by the
second selection unit 903.

Conclusion

[0153] According to the configuration of the content distribution system
40 pertaining to embodiment 1, the management of a content in the content
distribution system 40 is performed according to a method for controlling
the use of the content which is determined according to whether or not
the content-using device 900 is connected with the content management
server 800. As such, protection of the content, which has been provided
by a provider, is realized while a user utilizing the content is able to
use the content with an enhanced degree of convenience.

[0154] (2) When the second connection detection unit 901 detects that the
content-using device 900 has transitioned from being connected with the
content management server 800 to being unconnected with the content
management server 800, the second selection unit 903 may specify, as the
method for controlling the use of the content, a method according to a
period of validity of the content, and the content control unit 902 may
set a specific period of validity with respect to the content and, when
the specific period of validity of the content expires, may stop or deny
the use of the content.

[0155] When the first connection detection unit 802 detects that the
content management server 800 has transitioned from being connected with
the content-using device 900 to being unconnected with the content-using
device 900, the content management unit 801 may manage the content by
using the method according to a period of validity of the content and may
set a specific period of validity with respect to the content.

[0156] (3) When the second connection detection unit 901 detects that the
content-using device 900 has transitioned from being unconnected with the
content management server 800 to being connected with the content
management server 800, the second selection unit 903 may specify, as the
method for controlling the use of the content, a method independent of a
period of validity of the content, and the content control unit 902 may
cancel a specific period of validity set with respect to the content.

[0157] When the first connection detection unit 802 detects that the
content management server 800 has transitioned from being unconnected
with the content-using device 900 to being connected with the
content-using device 900, the content management unit 801 may manage the
content by using the method independent of a period of validity of the
content, and may cancel a specific period of validity set with respect to
the content.

[0158] (4) When the second connection detection unit 901 continuously
detects that the content-using device 900 is connected with the content
management server 800, the second selection unit 903 may continuously
specify, as the method for controlling the use of the content, a method
according to a period of validity of the content, and the content control
unit 902 may perform updating of extending a specific period of validity
set with respect to the content.

[0159] When the first connection detection unit 802 continuously detects
that the content management server 800 is connected with the
content-using device 900, the content management unit 801 may
continuously manage the content by using the method according to a period
of validity of the content and may perform updating of extending a
specific period of validity set with respect to the content.

[0160] (5) The content management server 800 may further comprise: an
invalidation reception unit that receives an invalidation instruction for
invalidation of the content; an invalidation instruction transmission
unit that transmits the invalidation instruction to the content-using
device 900; and an invalidation response reception unit that receives,
from the content-using device 900, an invalidation response as a response
to the invalidation instruction.

[0161] The content-using device 900 may further comprise: an invalidation
instruction reception unit that receives the invalidation instruction
from the content management server 800 when the content-using device 900
is connected with the content management server 800; an invalidation unit
that invalidates the content according to the invalidation instruction;
and an invalidation response transmission unit that generates an
invalidation response when the content has been invalidated and transmits
the invalidation response to the content management server 800.

[0162] The second selection unit 903 may specify, as the method for
controlling the use of the content, a method according to a period of
validity of the content when the content-using device 900 is unconnected
with the content management server 800, the content control unit 902 may
set a specific period of validity with respect to the content, and the
invalidation unit may invalidate the content when the specific period of
validity of the content expires.

[0163] (6) The content-using device 900 may further comprise a content
deletion unit that deletes the content.

[0164] The content control unit 902 may further record information
indicating deletion of the content when the content deletion unit has
deleted the content.

[0165] The content-using device 900 may further comprise a notification
unit that, (i) when the content-using device 900 is connected with the
content management server 800 and the content deletion unit has deleted
the content, immediately notifies the content management server 800 of
the deletion of the content and (ii) when the content-using device 900 is
unconnected with the content management server 800 and the content
deletion unit has deleted the content, notifies the content management
server 800 of the deletion of the content after the content-using device
900 is connected with the content management server 800.

[0166] The content management unit 801 may further record the deletion of
the content.

[0167] (7) One aspect of the present invention is the content management
server 800 managing a content and providing the content to the
content-using device 900. As illustrated in FIG. 1, the content
management server 800 comprises: the first connection detection unit 802
that detects whether or not the content management server 800 is
connected with the content-using device 900; and the content management
unit 801 that manages the content according to a result of the detection
by the first connection detection unit 802 and holds information on how
the content-using device 900 controls the use of the content.

[0168] (8) When the first connection detection unit 802 detects that the
content management server 800 has transitioned from being connected with
the content-using device 900 to being unconnected with the content-using
device 900, the content management unit 801 may manage the content by
using a method according to a period of validity of the content and may
set a specific period of validity with respect to the content.

[0169] (9) When the first connection detection unit 802 detects that the
content management server 800 has transitioned from being unconnected
with the content-using device 900 to being connected with the
content-using device 900, the content management unit 801 may manage the
content by using a method independent of a period of validity of the
content, and may cancel a specific period of validity set with respect to
the content.

[0170] (10) When the first connection detection unit 802 continuously
detects that the content management server 800 is connected with the
content-using device 900, the content management unit 801 may
continuously manage the content by using the method according to a period
of validity of the content and may perform updating of extending a
specific period of validity set with respect to the content.

[0171] (11) The first connection detection unit 802 may perform polling
with respect to the content-using device 900 at a predetermining timing,
may detect that the content management server 800 is connected with the
content-using device 900 when receiving a polling response from the
content-using device 900 in response to the polling, and may detect that
the content management server 800 is unconnected with the content-using
device 900 when the polling response is not received from the
content-using device 900 within a predetermined interval.

[0172] (12) The first connection detection unit 802 may determine the
predetermined timing according to a period of validity of the content.

[0173] (13) The first connection detection unit 802, when receiving a
polling signal from the content-using device 900 at a predetermined
timing, may detect that the content management server 800 is connected
with the content-using device 900, and may transmit a polling response to
the content-using device 900.

[0174] (14) The first connection detection unit 802 may detect that the
content management server 800 is connected with the content-using device
900 when receiving a notification from the content-using device 900 that
the content-using device 900 is connected with the content management
server 800.

[0175] (15) The content management server 800 may further comprise: an
invalidation reception unit that receives an invalidation instruction for
invalidation of the content; an invalidation instruction transmission
unit that transmits the invalidation instruction to the content-using
device 900; and an invalidation response reception unit that receives,
from the content-using device 900, an invalidation response as a response
to the invalidation instruction.

[0176] (16) The content management server 800 may further comprise a
display unit that displays a status of the invalidation of the content
performed according to the invalidation instruction by referring to the
invalidation response received from the content-using device 900. The
display unit, (i) may display invalidation completion information
indicating that the invalidation of the content has been completed by the
content-using device 900, when connected with the content management
server 800, and, (ii) may display a period of validity of the content set
in the content-using device 900, when unconnected with the content
management server 800.

[0177] (17) The content management server 800 may further comprise a
display unit that displays how the management of the content is being
performed.

[0178] (18) One aspect of the present invention is the content-using
device 900 that uses a content provided from the content management
server 800 managing the content.

[0179] As illustrated in FIG. 1, the content-using device 900 comprises:
the second connection detection unit 901 that detects whether or not the
content-using device 900 is connected with the content management server
800; the second selection unit 903 that specifies a method for
controlling the use of the content according to a result of the detection
by the second connection detection unit 901; and the content control unit
902 that controls the use of the content according to the method
specified by the second selection unit 903.

[0180] (19) When the second connection detection unit 901 detects that the
content-using device 900 has transitioned from being connected with the
content management server 800 to being unconnected with the content
management server 800, the second selection unit 903 specifies, as a
method for controlling the use of the content, a method according to a
period of validity of the content, and the content control unit 902 may
set a specific period of validity with respect to the content and, when
the specific period of validity of the content expires, may stop or deny
the use of the content.

[0181] (20) When the second connection detection unit 901 detects that the
content-using device 900 has transitioned from being unconnected with the
content management server 800 to being connected with the content
management server 800, the second selection unit 903 may specify, as the
method for controlling the use of the content, a method independent of a
period of validity of the content, and the content control unit 902 may
cancel a specific period of validity set with respect to the content.

[0182] (21) When the second connection detection unit 901 continuously
detects that the content-using device 900 is connected with the content
management server 800, the second selection unit 903 may continuously
specify, as the method for controlling the use of the content, a method
according to a period of validity of the content, and the content control
unit 902 may perform updating of extending a specific period of validity
set with respect to the content.

[0183] (22) The second connection detection unit 901 may detect whether or
not the content-using device 900 is connected with the content management
server 800 by performing either one of or any combination of: (i)
detecting, at a predetermined timing, whether or not a polling signal is
received from the content management server 800 at the predetermining
timing; (ii) detecting whether or not a communication module provided to
the content-using device 900 is activated; (iii) detecting whether or not
the content-using device 900 is located within a distance, from an access
point, within which radio signals from the content-using device 900 reach
the access point; and (iv) detecting whether a user operation is
performed with respect to the content-using device 900 for activating or
deactivating communication by the content-using device 900.

[0184] (23) The second connection detection unit 901, when detecting that
the content-using device 900 is connected with the content management
server 800, may perform polling with respect to the content management
server 800 and may receive a polling response from the content management
server 800 as a response to the polling.

[0185] The content control unit 902, when the polling response permits
extension of a period of validity set with respect to the content, may
perform updating of extending the period of validity.

[0186] (24) The second connection detection unit 901 may determine a
timing at which the polling is performed according to the period of
validity.

[0187] (25) The second connection detection unit 901, when detecting that
the content-using device 900 is connected with the content management
server 800, may transmit a notification to the content management server
800 that the content-using device 900 is connected with the content
management server 800.

[0188] The second connection detection unit 901 may detect whether or not
the content-using device 900 is connected with the content management
server 800 by performing either one of or any combination of: (i)
detecting, at a predetermined timing, whether or not a polling signal is
received from the content management server 800 at the predetermining
timing; (ii) detecting whether or not a communication module provided to
the content-using device 900 is activated; (iii) detecting whether or not
the content-using device 900 is located within a distance, from an access
point, within which radio signals from the content-using device 900 reach
the access point; and (iv) detecting whether a user operation is
performed with respect to the content-using device 900 for activating or
deactivating communication by the content-using device 900.

[0189] (26) The content-using device 900 may further comprise: an
invalidation instruction reception unit that receives an invalidation
instruction from the content management server 800 when the content-using
device 900 is connected with the content management server 800; an
invalidation unit that invalidates the content according to the
invalidation instruction; and an invalidation response transmission unit
that generates an invalidation response when the content has been
invalidated and transmits the invalidation response to the content
management server 800.

[0190] (27) The content-using device 900 may further comprise: a display
unit that displays a record of the invalidation of the content performed
according to the invalidation instruction when the invalidation unit has
invalidated the content.

[0191] (28) The content-using device 900 may further comprise a display
unit that displays how the control of the use of the content is being
performed by the content control unit 902.

[0192] (29) The content-using device 900 may further comprise: an
invalidation instruction reception unit that receives the invalidation
instruction from the content management server 800 when the content-using
device 900 is connected with the content management server 800; an
invalidation unit that invalidates the content according to the
invalidation instruction; and an invalidation response transmission unit
that generates an invalidation response when the content has been
invalidated and transmits the invalidation response to the content
management server 800.

[0193] The second selection unit 903 may specify, as the method for
controlling the use of the content, a method according to a period of
validity of the content when the content-using device 900 is unconnected
with the content management server 800, the content control unit 902 may
set a specific period of validity with respect to the content.

[0194] The invalidation unit may invalidate the content when the specific
period of validity of the content expires.

[0195] (30) The content-using device 900 may further comprise a content
deletion unit that deletes the content.

[0196] The content control unit 902 may further record information
indicating deletion of the content when the content deletion unit has
deleted the content.

[0197] The content-using device 900 may further comprise a notification
unit that, (i) when the content-using device 900 is connected with the
content management server 800 and the content deletion unit has deleted
the content, immediately notifies the content management server 800 of
the deletion of the content and (ii) when the content-using device 900 is
unconnected with the content management server 800 and the content
deletion unit has deleted the content, notifies the content management
server 800 of the deletion of the content after the content-using device
900 is connected with the content management server 800.

[0198] (31) One aspect of the present invention is control method used in
the content distribution system 40 including: the content management
server 800 that manages a content; and the content-using device 900 that
uses the content.

[0199] The control method comprises: a first connection detection step, by
the content management server 800, of detecting whether or not the
content management server 800 is connected with the content-using device
900; a content management step, by the content management server 800, of
managing the content according to a result of the detection in the first
connection detection step and of holding information on how the
content-using device 900 controls the use of the content; a second
connection detection step, by the content-using device 900, of detecting
whether or not the content-using device 900 is connected with the content
management server 800; a second selection step, by the content-using
device 900, of specifying a method for controlling the use of the content
according to a result of the detection in the second connection detection
step; and a content control step, by the content-using device 900, of
controlling the use of the content according to the method specified in
the second selection step.

[0200] (32) One aspect of the present invention is an integrated circuit
that forms the content management server 800 managing a content and
providing the content to the content-using device 900.

[0201] The integrated circuit comprises: a first connection detection unit
that detects whether or not the content management server 800 is
connected with the content-using device 900; and a content management
unit that manages the content according to a result of the detection by
the first connection detection unit and holds information on how the
content-using device 900 controls the use of the content.

[0202] (33) One aspect of the present invention is an integrated circuit
that forms the content-using device 900 that uses a content provided from
the content management server 800 managing the content.

[0203] The integrated circuit comprises: a second connection detection
unit that detects whether or not the content-using device 900 is
connected with the content management server 800; a second selection unit
that specifies a method for controlling the use of the content according
to a result of the detection by the second connection detection unit; and
a content control unit that controls the use of the content according to
the method specified by the second selection unit.

2. Embodiment 2

[0204] In the following, description is provided on a content distribution
system 10 pertaining to embodiment 2 of the present invention, with
reference to the accompanying drawings.

[0205] 2.1 Configuration of Content Distribution System 10

[0206]FIG. 2 illustrates an overall configuration of the content
distribution system 10. The content distribution system 10 includes: a
content management server 100; a content-using device 200; and a
communication path 300 between the content management server 100 and the
content-using device 200. The communication path 300 may be an IP
communication network or a non-IP communication network, may be a
wireline communication network or a wireless communication network, and
may include one or more communication devices such as a router interposed
between the content management server 100 and the content-using device
200. The content distribution system 10 may include two or more content
management servers and two or more content-using devices. When multiple
content management servers and multiple content-using devices are
included in the content distribution system 10, the content management
servers and the content-using devices may be interconnected via a
network.

[0209] Commonly, the content management server 100 is implemented as an
embedded device such as a PC and a video recorder. An embedded device
such as a PC and a video recorder includes: a CPU; a memory; a secondary
storage device; and a network interface. In the content management server
100, when implemented as such an embedded device, the online/offline
detection unit 101 is implemented as a combination of the network
interface, the CPU, and a program that operates on the CPU. Similarly,
the device management unit 102 is implemented as a combination of the
CPU, the memory, and a program that operates on the CPU. Similarly, the
content management unit 103 is implemented as a combination of the CPU,
the secondary storage device, and a program that operates on the CPU, and
the time measurement unit 104 is commonly implemented as a combination of
hardware such as a timer and software for controlling the hardware.
However, as a matter of course, the content management server 100
pertaining to the present embodiment is not limited to being implemented
in such a manner.

[0210] 2.2.1 Online/Offline Detection Unit 101

[0211]FIG. 3 illustrates a configuration of the online/offline detection
unit 101. The online/offline detection unit 101 detects that a device (a
content-using device) has transitioned from a state of being connected
with the content management server 100 (hereinafter a content-using
device, when in such a state, is referred to as being "online" or as an
"online content-using device") to a state of being unconnected with the
content management server 100 (hereinafter a content-using device, when
in such a state, is referred to as being "offline" or as an "offline
content-using device"). The online/offline detection unit 101 also
detects that the content-using device has transitioned from offline to
online. More specifically, the online/offline detection unit 101
includes: a polling transmission unit 110; an online/offline control
determination unit 112; a polling Ack reception unit 111; and an online
control reception unit 113.

[0212] The following provides specific description on how the
online/offline detection unit 101 detects whether the content-using
device is online or offline.

[0213] First, the online/offline control determination unit 112 notifies
the polling transmission unit 110 of an address of the content-using
device. The polling transmission unit 110 receives the address and
transmits a polling command to the address via the communication path
300. For instance, the transmission of the polling command is realized by
ping in an IP network. Ping is a software for testing the reachability of
a target node on an IP network. When utilizing ping, an Internet Control
Message Protocol (ICMP) "echo request" packet is transmitted to a target
node. Further, the reachability of the target node is confirmed by an
"echo reply" being returned from the target node as a response packet (a
polling Ack). With regards to the polling performed by the polling
transmission unit 110, the polling transmission unit 110 performs the
polling at regular intervals by being instructed by the online/offline
control determination unit 112. For instance, the polling is performed at
hourly intervals.

[0214] The polling Ack reception unit 111 receives a polling Ack returned
from the target node (i.e., the polling-target content-using device) as a
response to the polling command. When the polling Ack reception unit 111
receives the polling Ack, the online/offline control determination unit
112 determines that the target node is online. In contrast, when the
polling Ack reception unit 111 does not receive the polling Ack even
after elapse of a predetermined interval following the transmission of
the polling command (i.e., in cases of "timeout"), the online/offline
control determination unit 112 determines that the target node is
offline. The online/offline detection unit 101 transmits, at regular
intervals, a polling command to each content-using device to which a
content possessed by the content management server 100 has been
distributed. By performing the polling in such a manner, the
online/offline detection unit 101 detects whether each content-using
device is online or offline. Further, the online/offline detection unit
101 notifies the device management unit 102 of a result of the detection,
along with a detection time point at which the detection has been
performed.

[0215] As described above, in an IP network for instance, a given device
is determined as being online when, by utilizing ping, an "echo request"
(i.e., a polling command) is transmitted to the device and an "echo
reply" (i.e., a polling Ack (response)) corresponding to the "echo
request" is returned from the device in response. In contrast, a given
device is determined as being offline when, an "echo reply" (i.e., a
polling Ack (response)) corresponding to an "echo request" having been
transmitted to the device is not returned from the device.

[0216] The online control reception unit 113 also receives a notification
signal from a content-using device that self-detects a transition from
offline to online. Hereinafter, the notification signal transmitted and
received in such a case may also be referred to as an "online control
signal". When the online control reception unit 113 receives an online
control signal from a content-using device 200, the content management
server 100 determines that the content-using device 200 is online.

[0217] Once determining that the content-using device 200 is offline, the
content management server 100 stops performing online/offline detection,
which involves performing the polling at regular intervals, with respect
to the content-using device 200.

[0220] The device management control unit 120 controls the writing, the
reading out, and the deleting of content-using device information with
respect to the content-using device list 121. The device management
control unit 120 also controls the writing, the reading out, and the
deleting of offline device information with respect to the offline device
list 122. In addition, when, for instance, receiving an invalidation
instruction for invalidating playback of a content, the device management
control unit 120 reads out, from the content-using device list 121, an IP
address indicating a connection destination of a content-using device
corresponding to the invalidation instruction. Further, when it is
detected that a content-using device has transitioned from online to
offline as a result of the online/offline detection, the device
management control unit 120 adds, to the offline device list 122, offline
device information corresponding to the content-using device. Offline
device information corresponding to a given content-using device includes
a device name of the content-using device, etc. On the other hand, when
it is detected that a content-using device has transitioned from offline
to online as a result of the online/offline detection, the device
management control unit 120 deletes, from the offline device list 122,
offline device information corresponding to the content-using device,
which includes a device name of the content-using device, etc.

[0221]FIG. 5 is a chart indicating one example of a data configuration of
the content-using device list 121.

[0222] The content-using device list 121 is provided with areas for
storing multiple content-using device information pieces. Each
content-using device information piece includes, in an associated state,
a content-using device name and an IP address indicating a connection
destination of the content-using device. A content-using device name is
identification information identifying a content-using device. As such,
when a plurality of content-using device names are included in the
content-using device list 121, the content-using device names
respectively indicate a plurality of content-using devices that receives
a content from the content management server 100. Further, in this
example, a connection destination of a content-using device is indicated
by employing an IP address indicating a location on an IP network at
which the content-using device is located.

[0223] In the content-using device list 121 illustrated in FIG. 5, a
content-using device identified by "C1" in a content-using device name
field 124 is located on the IP network at a location indicated by
"192.168.1.21" in an IP address field 125. For instance, when instructing
the content-using device identified by the content-using device name "C1"
to invalidate playback, an invalidation instruction command is
transmitted to the IP address "192.168.1.21" indicated in the IP address
field 125. The same applies to content-using devices identified by
content-using device names "C2" and "C3". Here, in the content-using
device list 121 illustrated in FIG. 5, a private address such as
"192.168.*.*" is used to indicate an IP address. However, a global
address may be used to indicate an IP address. Further, although
indication of IP addresses in the content-using device list 121
illustrated in FIG. 5 is based on Internet Protocol Version 4 (IPv4),
alternatively, IP addresses may be indicated based on Internet Protocol
Version 6 (IPv6). In addition, taking into consideration the possibility
of an address of a content-using device being changed, a domain name may
be used instead of an IP address. Alternatively, also taking into
consideration the possibility of an IP address of a content-using device
being changed, configuration may be made such that an inquiry is made to
a server managing IP addresses.

[0224] Note that, in the present disclosure, a content-using device
identified by a content-using device name of "C1" may be simply referred
to as a content-using device "C1". The same applies to content management
servers.

[0225]FIG. 6 is a chart indicating one example of a data configuration of
the offline device list 122.

[0226] The offline device list 122 is provided with areas for storing
multiple offline device information pieces. Each offline device
information piece includes an offline device name and an offline
detection time. An offline device name identifies a content-using device
that has been determined by the online/offline detection unit 101 as
being offline. An offline detection time indicates a time point at which
the corresponding content-using device has been determined as being
offline by the online/offline detection unit 101.

[0227] The offline device list 122 illustrated in FIG. 6 indicates that a
content-using device identified by "C1" in an offline device name field
126 has been determined as being offline at "1/20, 00:00" in an offline
detection time field 127. Here, "1/20, 00:00" in the offline detection
time field 127 indicates 00:00, January 20th. In the following, the
same format is used for indications of time.

[0230] The content management control unit 130 controls the writing, the
reading out, and the deleting of management information with respect to
the content management list 131. For instance, in accordance with results
of the online/offline detection, the content management control unit 130
sets, in the content management list 131, a scheduled expiration time as
a time point at which a period of validity of a content expires.

[0231]FIG. 8 is a chart indicating one example of a data configuration of
the content management list 131.

[0232] The content management list 131 is provided with areas for storing
multiple management information pieces. Each management information piece
includes: one content ID; one relative validity duration; and either
zero, one, or multiple usage device information pieces. That is, a
management information piece includes either: (i) a combination of one
content ID and one relative validity duration; (ii) a combination of one
content ID, one relative validity duration, and one usage device
information piece; or (iii) a combination of one content ID, one relative
validity duration, and multiple usage device information pieces.

[0233] A management information piece including a combination of one
content ID and one relative validity duration indicates an initial state
of the management information. When a management information piece
indicates an initial state, the content management server 100 has not
provided a content to any content-using device. A management information
piece including a combination of one content ID, one relative validity
duration, and one usage device information piece indicates that the
content management server 100 has provided a content to only one
content-using device. A management information piece including a
combination of one content ID, one relative validity duration, and
multiple usage device information pieces indicates that the content
management server 100 has provided a content to the same number of
content-using devices as the number of usage device information pieces
included.

[0234] Each usage device information piece includes one content-using
device name or a combination of one content-using device name and one
scheduled expiration time. That is, a usage device information piece may
only include one content-using device name or may include a combination
of one content-using device name and one scheduled expiration time. When
a usage device information piece only includes one content-using device
name, a scheduled expiration time is not set with respect to the
content-using device identified by the content-using device name. When a
usage device information piece includes a combination of one
content-using device name and one scheduled expiration time, a scheduled
expiration time is set with respect to the content-using device
identified by the content-using device name.

[0235] A content ID uniquely identifies a corresponding content. A
relative validity duration indicates a relative duration during which
use, by an offline content-using device, of a content identified by the
corresponding content ID is permitted. Such a relative duration as
described above is referred to as a relative validity duration.

[0236] A content-using device name is a name identifying a content-using
device. A scheduled expiration time is included in a usage device
information piece when a content-using device identified by the
corresponding content-using device name is offline, and indicates a time
point at which a period of validity of the content expires. Here, the
content is referred to as being valid when use of the content by the
offline content-using device is permitted.

[0237] The content management list 131 illustrated in FIG. 8 indicates
that "24H", as indicated in a relative validity duration field 134, is
set as a relative validity duration of a content identified by "Cont 1"
in a content ID field 133. Here, "24H" indicates a time period of
twenty-four hours. The content management list 131 illustrated in FIG. 8
also indicates that the content "Cont1" is being used by two
content-using devices each indicated by "C1" in a content-using device
name field 135 and "C2" in a content-using device name field 136.

[0238] The content management list 131 illustrated in FIG. 8 indicates
that "1/21, 00:00", as indicated in a scheduled expiration time field
137, is set as a scheduled expiration time with respect to the
content-using device indicated by "C1" in the content-using device name
field 135. As such, the content-using device "C1" is currently offline
and the period of validity of the content "Cont1" with respect to the
content-using device "C1" expires at 00:00, January 21st. Here,
while a content is valid with respect to a given content-using device,
the content using device is permitted to use the content. This time point
at which the validity of the content "Cont1" expires is calculated by
adding "24H" indicated in the relative validity duration field 134 to
"1/20, 00:00" indicated in the offline detection time field 127
illustrated in FIG. 6. The indication of "1/21, 00:00" in the scheduled
expiration time field 137 indicates that the period of validity of the
content "Cont1" with respect to the content-using device "C1" expires at
this time point, if not sooner.

[0239] The content management list 131 illustrated in FIG. 8 indicates
that a scheduled expiration time is not set with respect to the
content-using device indicated by "C2" in the content-using device name
field 136. As such, the content-using device "C2" is currently online and
a specific period of validity of the content "Cont1" with respect to the
content-using device "C2" is not set. In the content management list 131
illustrated in FIG. 8, an indication of "---" is provided in a scheduled
expiration time field 138, which indicates that a scheduled expiration
time is not set.

[0240] The content management list 131 illustrated in FIG. 8 indicates
that "48H", as indicated in a relative validity duration field 140, is
set as a relative validity duration of a content identified by "Cont2" in
a content ID field 139. The content management list 131 illustrated in
FIG. 8 also indicates that the content "Cont2" is being used by two
content-using devices each indicated by "C1" in a content-using device
name field 141 and "C3" in a content-using device name field 142. Here,
"48H" indicates a time period of forty-eight hours. The content-using
device "C1" is currently offline, and "1/21, 00:00", as indicated in a
scheduled expiration time field 143, is set as a scheduled expiration
time with respect to the content-using device "C1". The content-using
device "C3" is currently online.

[0241]FIG. 9 is a chart indicating one example of a data configuration of
a content management list 131a, which is another example of the content
management list 131. In specific, the content management list 131a
indicates a state of the content management list 131 after the
content-using device "C1", which is offline in the content management
list 131 illustrated in FIG. 8, has transitioned from offline to online.
The content management list 131a indicates that each of the content-using
devices "C1", "C2", and "C3" is currently online. Further, the content
management list 131a indicates that a scheduled expiration time is not
set with respect to any of the content-using devices "C1", "C2", and
"C3".

[0242] 2.2.4 Time Measurement Unit 104

[0243] The time measurement unit 104 measures and outputs a current time.

[0244] 2.3 Content-Using Device 200

[0245]FIG. 2 illustrates a configuration of the content-using device 200.
The content-using device 200 includes: an online/offline notification
detection unit 201; a content control unit 202; and a time measurement
unit 203.

[0246] The content-using device 200 is commonly implemented as an embedded
device such as a PC and a mobile phone. An embedded device such as a PC
and a mobile phone includes a CPU, a memory, a secondary storage device,
and a network interface. In the content-using device 200, when
implemented as such an embedded device, the online/offline notification
detection unit 201 is implemented as a combination of the network
interface, the CPU, and a program that operates on the CPU. Similarly,
the content control unit 202 is implemented as a combination of the CPU,
the secondary storage device, and a program that operates on the CPU.
Further, the time measurement unit 203 is commonly implemented as a
combination of hardware such as a timer and software for controlling the
hardware. However, as a matter of course, the content-using device 200
pertaining to the present embodiment is not limited to being implemented
in such a manner.

[0249] When the content-using device 200 is online, the polling reception
unit 210 receives a polling command from the content management server
100.

[0250] Within a predetermined interval from the reception of the polling
command, the polling Ack transmission unit 211 generates a polling Ack
indicating that the content-using device 200 is online. The polling Ack
transmission unit 211 transmits the polling Ack to the content management
server 100. Here, the predetermined interval is, for instance,
one-hundred milliseconds. Alternatively, the predetermined interval may
be two-hundred milliseconds, three-hundred milliseconds, etc.

[0251] The online/offline control determination unit 212 determines
whether the content-using device 200 is online or offline. That is, the
online/offline control detection determination unit 212 detects a
transition of the content-using device 200 from online to offline.
Similarly, the online/offline control detection determination unit 212
also detects a transition of the content-using device from offline to
online.

[0252] For instance, the online/offline control determination unit 212 may
perform the determination as described above based on whether or not a
polling command is received from the content management server 100. In
specific, the online/offline control determination unit 212 determines
that the content-using device 200 is online when a polling command is
received from the content management server 100, while the online/offline
control determination unit 212 determines that the content-using device
200 is offline when a polling command is not received from the content
management server 100.

[0253] Alternatively, the online/offline control determination unit 212
may determine that the content-using device 200 is online when a
communication module in the content-using device 200 is activated. In
such a case, the online/offline control determination unit 212 determines
that the content-using device 200 is offline when the communication
module is deactivated.

[0254] Further, when wireless communication is performed with the content
management server 100, the online/offline control determination unit 212
may perform the determination as described in the following. The
online/offline control determination unit 212 determines that the
content-using device 200 is online when the content-using device 200 is
located within a distance from an access point within which radio signals
transmitted from the content-using device 200 reach the access point.
Further, the online/offline control determination unit 212 determines
that the content-using device 200 is offline when the content-using
device 200 is not located within a distance from an access point within
which radio signals transmitted from the content-using device 200 reach
the access point. That is, the online/offline control determination unit
212 determines that the content-using device 200 is offline when radio
signals transmitted from the content-using device 200 do not reach an
access point.

[0255] The online/offline control determination unit 212, at a time point
when a transition from offline to online is detected, notifies the online
control transmission unit 213 of a result of the detection. When
receiving the detection result from the online/offline control
determination unit 212, the online control transmission unit 213
transmits the detection result, which indicates that the content-using
device 200 has transitioned from offline to online, to the content
management server 100.

[0259] The content storage unit 224 stores a content. The content has been
provided from the content management server 100.

[0260] The content management control unit 221 manages the content stored
in the content-using device 200 by using the content management list 222,
detailed description of which is provided in the following.

[0261] The content usage control unit 223, by being controlled by the
content management control unit 221, determines whether or not the
content-using device 200 has a right to use the content. When the
content-using device 200 has the right to use the content, and further,
is permitted to use the content, the content usage control unit 223
causes the content playback unit 226 to play back the corresponding
content stored in the content storage unit 224. Further, when the
content-using device 200 is offline, the content usage control unit 223
reads out, from the content management list 222, a content management
information piece including a content ID identifying the content.
Subsequently, the content usage control unit 223 extracts a scheduled
expiration time from the content management information piece read out,
and determines whether or not a period of validity as indicated by the
scheduled expiration time, has expired. When the period of validity
indicated by the scheduled expiration time has already expired, the
content usage control unit 223 stops the use of the content. When the
period of validity indicated by the scheduled expiration time has not
expired, the content usage control unit 223 permits the use of the
content.

[0262] The content playback unit 226, by being controlled by the content
usage control unit 223, reads out the content stored in the content
storage unit 224 and plays back the content read out.

[0263]FIG. 12 is a chart indicating one example of a data configuration
of the content management list 222.

[0264] The content management list 222 is provided with areas for storing
multiple content management information pieces. Each content management
information piece includes either: (i) a combination of one content ID,
one relative validity duration, one content management server name, and
one scheduled expiration time; or (ii) a combination of one content ID,
one relative validity duration, and one content management server name.
As such, a content management information piece may include or may not
include a scheduled expiration time.

[0265] A content ID is identification information identifying a content. A
relative validity duration associated with a corresponding content ID
indicates a relative period during which use, by the content-using device
200 in offline state, of the content identified by the corresponding
content ID is permitted. A content management server name associated with
a corresponding content ID identifies a content management server from
which the content identified by the corresponding content ID has been
transmitted. A scheduled expiration time associated with a corresponding
content ID indicates a time point at which validity of use, by the
content-using device 200 in offline state, of the content identified by
the corresponding content ID expires. A scheduled expiration time is
calculated when the content-using device 200 transitions from online to
offline by adding a corresponding relative validity duration to the time
point at which the content-using device 200 has transitioned from online
to offline.

Scheduled Expiration Time=Time Point at which Content-using Device
Transitioned from Online to Offline+Relative Validity Period

[0266] When the period of validity indicated by the scheduled expiration
time has already passed at the point when the content-using device 200
transitions from online to offline, the use, by the content-using device
200 in offline state, of the content identified by the corresponding
content ID is prohibited.

[0268] The content management information piece 266 includes: "Cont1" in a
content ID field 251; "24H" in a relative validity duration field 252;
"S1" in a content management server name field 253; and "1/20, 23:30" in
an scheduled expiration time field 254. The content management
information piece 266 indicates that the content identified by "Cont1" in
the content ID field 251 has been supplied from the content management
server identified by "S1" in the content management server name field
253. The content-using device 200 is currently offline. "1/20, 23:30", as
indicated in the scheduled expiration time field 254, is set as the time
point at which the validity of the content identified by "Cont1" in the
content ID field 251 expires. Here, the indication of "1/20, 23:30" in
the scheduled expiration time field 254 indicates that the period of
validity of the content "Cont1" expires at 23:30, January 20th.
"1/20, 23:30" in the scheduled expiration time field 254 is calculated by
adding "24H" in the corresponding relative validity duration field 252 to
the time point at which the content-using device 200 has transitioned
from online to offline.

[0269] The content management information piece 267 includes: "Cont2" in a
content ID field 255; "48H" in a relative validity duration field 256;
"S1" in a content management server name field 257; and "1/21, 23:30" in
a scheduled expiration time field 258. The content management information
piece 267 indicates that the content identified by "Cont2" in the content
ID field 255 has been supplied from the content management server
identified by "S1" in the content management server name field 257,
similar as the content "Cont1". Here, the indication of "1/21, 23:30" in
the scheduled expiration time field 258 indicates that the period of
validity of the content "Cont2" expires at 23:30, January 21st.
"1/21, 23:30" in the scheduled expiration time field 258 is calculated by
adding "48H" in the corresponding relative validity duration field 256 to
the time point at which the content-using device 200 has transitioned
from online to offline.

[0270] The content management information piece 268 includes: "Cont3" in a
content ID field 259; "24H" in a relative validity duration field 260;
"S2" in a content management server name field 261; and "1/20, 23:30" in
a scheduled expiration time field 262. The content management information
piece 268 indicates that the content identified by "Cont3" in the content
ID field 259 has been supplied from the content management server
identified by "S2" in the content management server name field 261.

[0271]FIG. 13 is a chart indicating one example of a data configuration
of a content management list 222a, which is another example of the
content management list 222. For instance, the content management list
222a in FIG. 13 includes a content management information piece 266a, a
content management information piece 267a, and a content management
information piece 268a. The content management list 222a differs from the
content management list 222 illustrated in FIG. 12 in that the content
management information pieces 266a, 267a, and 268a included therein
indicate that the content-using device 200 is currently online.

[0272] Each of the content management information pieces 266a, 267a, and
268a does not include a scheduled expiration time. That is, as indicated
by the content management information pieces 266a, 267a, and 268a, a
scheduled expiration time is not set with respect to each of contents
identified by "Cont1" in the content ID field 251, "Cont2" in the content
ID field 255, and "Cont3" in the content ID field 259. As such, a
specific period of validity is not set with respect to each of such
contents, and therefore, the content-using device 200, which is currently
online, is permitted to use such contents for an unlimited period of
time.

[0273] 2.3.3 Time Measurement Unit 203

[0274] The time measurement unit 203 measures and outputs the current
time.

[0275] 2.4 Operations of Content Distribution System 10 (Part 1)

[0276] In the following, description is provided on operations of the
content distribution system 10.

[0277] (1) Here, description is provided on operations of the content
distribution system 10 when the content management server 100 detects
whether the content-using device 200 is online or offline, with reference
to sequence diagrams illustrated in FIGS. 14 through 16.

[0278] Once the online/offline control determination unit 112 determines
that the content-using device 200 is offline ("NO" in Step S131), content
management server 100 stops performing the detection of whether the
content-using device is online or offline (Step S132).

[0279] When determining that the content-using device 200 is online ("YES"
in Step S131), the online/offline control determination unit 112 outputs,
to the polling transmission unit 110, an address and an instruction
instructing the polling transmission unit 110 to perform polling (Step
S133). When receiving the address and the polling instruction, the
polling transmission unit 110 transmits a polling command to the
content-using device 200 (Step S134).

[0282] The online/offline control determination unit 112, when receiving
the polling Ack within a predetermined interval after outputting the
polling instruction ("NO" in Step S140), determines that the
content-using device 200 is online (Step S141). That is, the
online/offline control determination unit 112 determines that the
content-using device 200 is online when no timeout occurs. Here, the
predetermined interval is, for instance, one second. Alternatively, the
predetermined interval may be five-hundred milliseconds, six-hundred
milliseconds, seven-hundred milliseconds, etc.

[0283] In contrast, the online/offline control determination unit 112,
when receiving the polling Ack after the predetermined interval has
elapsed from the output of the polling instruction or when not receiving
a polling Ack ("YES" in Step S140), determines that the content-using
device 200 is offline (Step S142). That is, the online/offline control
determination unit 112 determines that the content-using device 200 is
offline when timeout occurs.

[0284] Subsequently, the online/offline control determination unit 112
outputs, to the device management control unit 120, a transmission source
IP address, a detection time, and a detection result (Step S143).

[0285] The device management control unit 120 receives, from the
online/offline control determination unit 112, the transmission source IP
address, the detection time, and the detection result (Step S143).

[0286] Subsequently, the device management control unit 120 reads out,
from the content-using device list 121, a content-using device name
corresponding to the transmission source IP address received (Step S144).

[0288] When the detection result indicates online ("Online" in Step S145),
the device management control unit 120 deletes, from the offline device
list 122, an offline device information piece including the same offline
device name as the content-using device name read out from the
content-using device list 121 (Step S146).

[0289] When the detection result indicates offline ("Offline" in Step
S145), the device management control unit 120 generates an offline device
information piece. The offline device information generated includes the
content-using device name read out as an offline device name and includes
the detection time received as an offline detection time. Subsequently,
the device management control unit 120 adds the offline device
information piece generated to the offline device list 122 (Step S147).

[0290] Subsequently, the device management control unit 120 outputs, to
the content management control unit 130, the content-using device name
read out, the detection time received, and the detection result received
(Step S148).

[0291] In addition to the above, the device management control unit 120,
when receiving an invalidation instruction for invalidating playback of a
content (Step S149), reads out, from the content-using device list 121,
an IP address of a connection-destination content-using device (Step
S150).

[0292] When the device management control unit 120 outputs the
content-using device name, the detection time, and the detection result,
the content management control unit 130 receives the content-using device
name, the detection time, and the detection result from the device
management control unit 120 (Step S148).

[0293] In addition to receiving such information from the device
management control unit 120, the content management control unit 130
receives content provision information from the content-using device 200
(Step S161). The content provision information includes a content ID and
a content-using device name.

[0294] When receiving the content provision information, the content
management control unit 130 generates a usage device information piece
including the content-using device name included in the content provision
information. Subsequently, the content management control unit 130 reads
out, from the content management list 131, a management information piece
indicated by the content ID included in the content provision
information. Subsequently, the content management control unit 130 writes
and adds, to the management information read out, the usage device
information piece generated (Step S162).

[0295] As already described above, the content management control unit 130
receives, from the device management control unit 120, the content-using
device name, the detection time, and the detection result (Step S148). In
addition, the content management control unit 130 receives, from the
content-using device 200, a result of a self-detection performed by the
content-using device 200 of whether the content-using device 200 is
online or offline (Step S164).

[0296] The content management control unit 130 determines whether the
detection result received indicates online or offline (Step S165).

[0297] When determining that the detection result received indicates
online ("Online" in Step S165), the content management control unit 130
tries to read out, from the content management list 131, a usage device
information piece including a content-using device name corresponding to
the content-using device 200 (Step S166).

[0298] When the reading out of the usage device information piece is
completed without reading being performed of the entire content
management list 131 ("NO" in Step S167), the content management control
unit 130 deletes an scheduled expiration time included in the usage
device information piece (Step S168). Following this, the content
management control unit 130 returns to Step S166.

[0299] When the reading out of the usage device information piece is not
completed even when reading has been performed of the entire content
management list 131 ("YES" in Step S167), the content management control
unit 130 proceeds to the subsequent step.

[0300] On the other hand, when determining that the detection result
received indicates offline ("Offline" in Step S165), the content
management control unit 130 tries to read out, from the content
management list 131, a usage device information piece including a
content-using device name corresponding to the content-using device 200
(Step S169).

[0301] When the reading out of the usage device information piece is
completed without reading being performed of the entire content
management list 131 ("NO" in Step S170), the content management control
unit 130 reads out, from the content management list 131, a relative
validity duration corresponding to a content ID. Then, the content
management control unit 130 performs the calculation of: scheduled
expiration time=detection time+relative validity duration (Step S172).
Subsequently, the content management control unit 130 writes, to the
content management list 131, the scheduled expiration time so calculated
in association with the content-using device name corresponding to the
content-using device 200 (Step S173). Following this, the content
management control unit 130 returns to Step S169.

[0302] When the reading out of the usage device information piece is not
completed even when reading has been performed of the entire content
management list 131 ("YES" in Step S170), the content management control
unit 130 proceeds to the subsequent step.

[0303] (2) Here, description is provided on operations of the content
distribution system 10 when the content-using device 200 receives a
content from the content management server 100, with reference to the
sequence diagram illustrated in FIG. 17.

[0304] The content management control unit 221 receives a content from the
content management server 100 (Step S301). Subsequently, the content
management control unit 221 outputs the content received to the content
usage control unit 223 (Step S302).

[0305] The content usage control unit 223 receives the content (Step
S302), and writes the content received to the content storage unit 224
(Step S303).

[0307] (3) Here, description is provided on operations of the
content-using device 200 in a case where the content-using device 200
performs self-detection of whether the content-using device 200 is online
or offline, with reference to the sequence diagrams illustrated in FIGS.
18 and 19.

[0309] When a result of the detection indicates a transition from offline
to online ("Offline to Online" in Step S182), the online/offline control
determination unit 212 outputs the detection result to the online control
transmission unit 213 (Step S183). The online control transmission unit
213 transmits the detection result to the content management server 100
(Step S184).

[0310] On the other hand, when the detection result indicates a transition
from online to offline ("Online to Offline" in Step S182), the
online/offline control determination unit 212 outputs the detection
result and a detection time at which the detection has been made to the
content management control unit 221 (Step S185).

[0311] The content management control unit 221 receives the detection time
and the detection result (Step S185). Subsequently, the content
management control unit 221 determines whether the detection result
received indicates a transition from online to offline or a transition
from offline to online (Step S311).

[0312] When the detection result indicates a transition from online to
offline ("Online to Offline" in Step S311), the content management
control unit 221 tries to read out, from the content management list 222,
a content management information piece (Step S312).

[0313] When the reading out of the content management information piece is
completed without reading being performed of the entire content
management list 222 ("NO" in Step S313), the content management control
unit 221 performs the calculation of: scheduled expiration time=detection
time+relative validity duration (Step S314). Subsequently, the content
management control unit 221 writes, to the content management list 222,
the scheduled expiration time calculated (Step S315). Following this,
processing proceeds to Step S312.

[0314] When the reading out of the content management information piece is
not completed even when reading has been performed of the entire content
management list 222 ("YES" in Step S313), the content management control
unit 221 proceeds to the subsequent step.

[0315] When the detection result indicates a transition from offline to
online ("Offline to Online" in Step S311), the content management control
unit 221 tries to read out, from the content management list 222, a
content management information piece (Step S316).

[0316] When the reading out of the content management information piece is
completed without reading being performed of the entire content
management list 222 ("NO" in Step S317), the content management control
unit 221 deletes a scheduled expiration time in the content management
information piece (Step S318). Following this, processing proceeds to
Step S316.

[0317] When the reading out of the content management information piece is
not completed even when reading has been performed of the entire content
management list 222 ("YES" in Step S317), the content management control
unit 221 proceeds to the subsequent step.

[0318] (4) Here, description is provided on operations of the
content-using device 200 when the content-using device 200 uses a
content, with reference to the sequence diagram illustrated in FIG. 20.

[0319] The content usage control unit 223 receives a content ID
corresponding to the content received from the content management server
100 (Step S331). Subsequently, the content usage control unit 223 reads
out, from the content management list 222, a content management
information piece including the content ID received (Step S332).

[0320] Subsequently, the content usage control unit 223 determines whether
or not the content management information piece read out includes a
scheduled expiration time (Step S333).

[0321] When the content management information piece read out includes a
scheduled expiration time ("Included" in Step S333), the content usage
control unit 223 determines whether the scheduled expiration time has
already passed (Step S334). When the scheduled expiration time has
already passed ("YES" in Step S334), the content usage control unit 223
generates an instruction for stopping the use of the content (Step S337).
Subsequently, the content usage control unit 223 outputs the instruction
for stopping the use of the content to the content playback unit 226
(Step S338).

[0322] When the scheduled expiration time has not passed yet ("NO" in Step
S334), the content usage control unit 223 generates an instruction for
permitting the use of the content (Step S335). Subsequently, the content
usage control unit 223 outputs the instruction for permitting the use of
the content to the content playback unit 226 (Step S336).

[0323] The content usage control unit 223 also determines whether the
content-using device 200 has the right to use the content (Step S339).
When determining that the content-using device 200 does not have the
right to use the content ("Not possessed" in Step S340), the content
usage control unit 223 generates an instruction for prohibiting the use
of the content (Step S341). Further, the content usage control unit 223
outputs the instruction for prohibiting the use of the content to the
content playback unit 226 (Step S342). When determining that the
content-using device 200 has the right to use the given content
("Possessed" in Step S340), the content usage control unit 223 generates
an instruction for permitting the use of the content (Step S343).
Subsequently, the content usage control unit 223 outputs the instruction
for permitting the use of the content to the content playback unit 226
(Step S344).

[0324] The content playback unit 226 determines whether the instruction
received from the content usage control unit 223 is an instruction for
permitting the use of the content, an instruction for prohibiting the use
of the content, or an instruction for stopping the use of the content
(Step S345). When an instruction for permitting the use of the content
has been received ("Permission" in Step S345), the content playback unit
226 plays back the content (Step S346). When an instruction for
prohibiting or stopping the use of the content has been received
("Prohibition or stop" in Step S345), the content playback unit 226 does
not play back the content.

[0325] 2.5 One Example of Configuration of Content Distribution System 10

[0326] FIG. 21 is a diagram illustrating a configuration of a content
distribution system 10a, which is one example of the content distribution
system 10 for providing an explanation of operations of the content
distribution system 10.

[0327] In this example, the content distribution system 10a includes two
content management servers and three content-using devices. More
specifically, the content distribution system 10a includes: a content
management server 100a (also referred to as a "content management server
S1"); a content management server 100b (also referred to as a "content
management server S2"); a content-using device 200a (also referred to as
a "content-using device C1"); a content-using device 200b (also referred
to as a "content-using device C2"); and a content-using device 200c (also
referred to as a "content-using device C3").

[0328] FIG. 21 illustrates how contents are shared between the content
management servers and the content-using devices. Further, FIG. 21 also
illustrates connections between the content management servers and the
content-using devices.

[0329] The content management server 100a provides a content identified by
a content name "Cont1" and a content identified by a content name
"Cont2". The content management server 100b provides a content identified
by a content name "Cont3".

[0330] The content-using device 200a is provided, by the content
management server 100a, with the contents "Cont1" and "Cont2". The
content-using device 200a is also provided, by the content management
server 100b, with the content "Cont3".

[0331] The content-using device 200b is provided, by the content
management server 100a, with the content "Cont1".

[0332] The content-using device 200c is provided, by the content
management server 100a, with the contents "Cont1" and "Cont2".

[0333] As such, the contents "Cont1" and "Cont2" are shared between the
content management server 100a and the content-using device 200a. That
is, the contents "Cont1" and "Cont2" possessed by the content management
server 100a are provided for use to the content-using device 200a.
Similarly, the content "Cont1" is shared between the content management
server 100a and the content-using device 200b. That is, the content
"Cont1" possessed by the content management server 100a is provided for
use to the content-using device 200b. Further, the contents "Cont1" and
"Cont2" are shared between the content management server 100a and the
content-using device 200c. That is, the contents "Cont1" and "Cont2"
possessed by the content management server 100a are provided for use to
the content-using device 200c.

[0334] In addition to the above, the content "Cont3" is shared between the
content management server 100b and the content-using device 200a. That
is, the content "Cont3" possessed by the content management server 100b
is provided for use to the content-using device 200a.

[0335] Here, the content possessed by the content management server 100b
is not used by the content-using device 200b. That is, as illustrated in
FIG. 21, the content management server 100b and the content-using device
200b are not connected with each other.

[0336] 2.6 Operations of Content Distribution System 10 (Part 2)

[0337] In the following, description is provided on operations of the
content distribution system 10, with reference to the sequence diagram
illustrated in FIG. 22.

[0338] Note that the following description focuses on the interaction
between the content management server 100a and the content-using device
200a, based on the configuration illustrated in FIG. 21.

[0339]FIG. 22 is a diagram illustrating the interaction between the
content management server 100a and the content-using device 200a in a
case where the content-using device 200a transitions from online to
offline during the interaction. Note that the content management server
100a transmits a polling command to each of the content-using devices
connected therewith at hourly intervals. By performing polling in such a
manner, the content management server 100a checks whether or not each of
the content-using devices is online.

[0340] Step 1) At 23:00, January 19th, the content management server
100a transmits a polling command to the content-using device 200a (Step
S101). The content-using device 200a, which is online at this point,
receives the polling command from the content management server 100a.
Within a predetermined interval from the reception of the polling
command, the content-using device 200a transmits a polling Ack to the
content management server 100a (Step S111). The content management server
100a receives the polling Ack and thereby confirms that the content-using
device 200a is online (Step S101).

[0341] At this point, the content-using device list 121 in the content
management server 100a includes, for each of content-using devices 200a,
200b, and 200c connected with the content management server 100a, a
content-using device name and an IP address in an associated state, as
illustrated in FIG. 5. On the other hand, no information is registered to
the offline device list 122 at this point.

[0342] Further, as indicated by the content management list 131a
illustrated in FIG. 9, the content "Cont1" is being used by the
content-using devices 200a and 200b at this point. Similarly, as
indicated by the content management list 131a illustrated in FIG. 9, the
content "Cont2" is being used by the content-using devices 200a and 200c
at this point. Further, since each of the content-using devices 200a,
200b, and 200c is online at this point, the content management list 131a
includes an indication of "---" in the corresponding scheduled expiration
time field. The indication of "---" in a scheduled expiration time field
indicates that a scheduled expiration time is not set. In addition, the
content management list 222a as illustrated in FIG. 13 indicates the
content management list held by the content-using device 200a at this
point. Since the content-using device 200a is online at this point, each
of the content management information pieces included in the content
management list 222a does not include a scheduled expiration time. More
specifically, the content management list 222a indicates that the
content-using device 200a is using the contents "Cont1" and "Cont2"
possessed by the content management server 100a and the content "Cont3"
possessed by the content management server 100b. Further, the
content-using device 100a is permitted to use each of such contents for
an unlimited period of time.

[0343] Step 2) At 23:30, January 19th (time point T01), the
content-using device 200a transitions from online to offline. This is due
to, for instance, the content-using device 200a having moved to a
location where radio signals cannot reach or the content-using device
200a having deactivated a communication module therein. The content-using
device 200a self-detects the transition from online to offline, or that
is, the online/offline control determination unit 212 detects the
transition from online to offline, and notifies the content control unit
202 of the transition from online to offline. The content control unit
202 performs updating of the content management list held by the
content-using device 200a (Step S112). For instance, the content control
unit 202 performs the updating such that the content management list 222a
in FIG. 13, which corresponds to before the transition from online to
offline, is replaced with the content management list 222 in FIG. 12.

[0344] In specific, in the content management list 222 in FIG. 12, the
content management information piece 266 including "Cont1" in the content
ID field 251 is updated such that "1/20, 23:30", which indicates 23:30,
January 20th, is set to the scheduled expiration time field 254.
"1/20, 23:30" is calculated by adding "24H" in the relative validity
duration field 252 to 23:30, January 19th, which is the time point
at which the content-using device 200a transitioned from online to
offline. Similarly, in the content management list 222, the content
management information piece 267 including "Cont2" in the content ID
field 255 is updated such that "1/21, 23:30", which indicates 23:30,
January 21st, is set to the scheduled expiration time field 258.
"1/21, 23:30" is calculated by adding "48H" in the relative validity
duration field 256 to the time point at which the content-using device
200a transitioned from online to offline. In addition, in the content
management list 222, the content management information piece 268
including "Cont3" in the content ID field 259 is updated such that "1/20,
23:30" is set to the scheduled expiration time field 262. "1/20, 23:30"
is calculated by adding "24H" in the relative validity duration field 260
to the time point at which the content-using device 200a transitioned
from online to offline.

[0345] The content usage control unit 223 controls the use of the contents
"Cont1", "Cont2", and "Cont3" by referring to the scheduled expiration
times set in the content management list 222. For instance, the content
usage control unit 223, while monitoring the current time, controls the
use of the content identified by the content ID "Cont1" such that the use
of the content "Cont1" is stopped when the scheduled expiration time
"1/20, 23:30" (time point T02) is reached. Here, the stopping of the use
of a given content refers to either (i) canceling the display of the
content or (ii) canceling the display of the content, and further,
deleting the content having been expanded on the RAM from the RAM, in
response to a timer interrupt notification indicating that the scheduled
expiration time has been reached.

[0346] In the following, description is provided on other types of control
that may be performed when stopping the use of a given content at a point
when the corresponding scheduled expiration time being reached. For
instance, when a user is viewing the given content at the point when the
scheduled expiration time is reached, the user may feel disappointed if
the display of the content is suddenly cancelled and disappears. As such,
control may be performed such that the use of the content currently under
progress is continued and the stopping of the use of the content is
performed when a page subsequent to the currently-displayed page is
displayed or when an application currently being launched is launched
once again. Further, so as to enhance user-friendliness, a notification
may be made to the user that a period of validity of the content has
expired after the use of the content is actually stopped. Alternatively,
the stopping of the use of the content may be performed at the same time
as notifying the user of the expiration of the period of validity of the
content.

[0347] Step 3) At 00:00, January 20th, the content management server
100a transmits a polling command to each of the content-using devices
connected therewith (Step S102). However, a polling Ack is not returned
from the content-using device 200a, which is offline at this point (Step
S103). In response to this, the content management server 100a registers,
to the offline device list 122 (illustrated in FIG. 6), the device name
"C1" of the content-using device 200a as an offline device name in
addition to a detection time ("1/20, 00:00") at which the content-using
device 200a has been detected as being offline (Step S104). Further, the
content management control unit 130 of the content management server 100a
searches the content management list 131 for a device name "C1" having
been registered to the offline device list 122 as an offline device name.
Subsequently, the content management control unit 130 sets, in the
content management list 131, a scheduled expiration time to each content
being provided to a content-using device identified by the device name
"C1". The contents being provided to the content-using device identified
by the device name "C1" are specified as a result of the above-described
search in the content management list 131. In this example, the content
management server 100a is providing contents "Cont1" and "Cont2" to the
content-using device identified by the device name "C1". More
specifically, in the content management list 131, "1/21, 00:00" is set as
the scheduled expiration time of the content "Cont1". "1/21, 00:00" is
calculated by adding the corresponding relative validity duration to the
offline detection time. Similarly, in the content management list 131,
"1/22, 00:00" is set as the scheduled expiration time of the content
"Cont2". "1/22, 00:00" is calculated by adding "48H", which is the
corresponding relative validity duration, to the offline detection time.
Here, it should be noted that "1/21, 00:00" set as the scheduled
expiration time of the content "Cont1" is actually thirty minutes later
than the time point "1/20, 23:30", at which the validity of the content
"Cont1" with respect to the content-using device 200a expires. However,
at the same time, it should be noted that the content "Cont1" is
invalidated by the content-using device 200a by this time point, if not
sooner. That is, "1/21, 00:00" set as the scheduled expiration time of
the content "Cont1" in the content management list 131 indicates that
playback of the content "Cont1" cannot be performed at least from this
time point onward.

[0348] 2.6 Operations of Content Distribution System 10 (Part 3)

[0349] In the following, description is provided on operations of the
content distribution system 10, with reference to the sequence diagram
illustrated in FIG. 23.

[0350] In the operations of the content distribution system 10 illustrated
in FIG. 22, the content-using device 200a transitions from online to
offline at 23:30, January 19th. FIG. 23 illustrates operations of
the content distribution system 10 following this point. More
specifically, FIG. 23 illustrates operations of the content distribution
system 10 in a case where, after 23:30, January 19th, the
content-using device 200a becomes online with respect to the content
management server 100a once again at 03:00, January 20th.

[0351] Step 4) At 03:00, January 20th (time point T03), the
content-using device 200a self-detects a transition from offline to
online. At this point, the user of the content-using device 200a
activates a communication module in the content-using device 200a or
moves the content-using device 200a to a location where radio signals can
reach the content-using device 200a. Due to this, content-using device
200a transitions from offline to online. The content-using device 200a,
via the online control transmission unit 213, notifies the content
management server 100a of the transition from offline to online (Step
S113). At the same time, the content-using device 200a, at time point
T04, sets an infinity value to each scheduled expiration time in the
content management list 222. When an infinity value is set to a scheduled
expiration time, the scheduled expiration time indicates that a specific
period of validity is not set with respect to the corresponding content.
As such, the content is made available for use whenever desired and for
an unlimited period of time. In other words, at time point T04, the
content-using device 200a deletes each scheduled expiration time in the
content management list 222, and thereby makes the corresponding contents
usable at any time following time point T04 while the content-using
device 200a (Step S114).

[0352] In the meantime, the content management server 100a receives, via
the online control reception unit 113, the notification from the
content-using device 200a indicating that the content-using device 200a
is online (Step S113). Subsequently, the content management server 100a
deletes, from the offline device list 122, an offline device information
piece including an offline device name "C1". In addition, the content
management server 100a also deletes, from a management information piece
including a content-using device name "C1" in the content management list
131, scheduled expiration times of the contents "Cont1" and "Cont2". As a
result, the content management list 131 is updated so as to indicate that
the content-using device 200a is online. More specifically, the content
management server 100a updates the content management list 131
illustrated in FIG. 8 by deleting the scheduled expiration times in the
scheduled expiration time fields 137 and 143. As a result of the
updating, the content management list 131a illustrated in FIG. 9 is
obtained (Step S105).

[0353] 2.7. Effects Achieved by Embodiment 2

[0354] In embodiment 2, the content management server performs polling
with respect to the content-using device at regular intervals, and
thereby performs detection of whether the content-using device is online
or offline. Due to this, the content-using device is able to perform
control based on a period of validity of a content after actually having
transitioned from online to offline. As such, a user is able to use the
content with the maximum degree of convenience.

[0355] Also, in embodiment 2, the content-using device automatically
detects (self-detects) transition from online to offline, and when
detecting the transition from online to offline, switches to performing
management of a content based on a period of validity of the content. On
the other hand, the content-using device, when detecting a transition
from offline to online, is able to stop performing management of the
content based on the period of validity of the content.

[0356] In the meantime, the content management server detects whether the
content-using device is online or offline according to whether or not a
polling Ack is received from the content-using device as a response to a
polling command. Further, the content management server, when the
content-using device transitions from offline to online, is able to
detect the transition from offline to online by receiving a notification
from the content-using device indicating that the content-using device is
online. As such, the content management server is able to perform the
management of the content in the same way as the management of the
content is performed by the content-using device.

[0357] As description has been provided above, opportunities are
increasing where photos and video contents are exchanged as development
of infrastructure supporting such exchange of personal contents
progresses. However, at the same time, a user who owns and provides a
content to others is concerned that the content he/she has provided may
be used in an undesirable or unintended manner at a distribution
destination, which includes unauthorized copying or leaking of the
content. So as to address such a concern, there is a demand for a
structure that enables the user, according to his/her intention,
invalidate the content having been provided to a distribution destination
and thereby disable the playback of the content at the distribution
destination.

[0358] In the content distribution system 10, the management of a content
is performed according to a method for controlling the use of the content
which is determined according to whether or not the content-using device
is connected with the content management server. As such, protection of
the content, which has been provided by a provider, is realized while a
user utilizing the content is able to use the content with an enhanced
degree of convenience. As such, users are able to provide the content to
others free of such concerns as described above.

3. Embodiment 3

[0359] In the following, description is provided on a content distribution
system 20 pertaining to another embodiment of the present invention, with
reference to the accompanying drawings.

[0360] 3.1 Overall Configuration of Content Distribution System 20

[0361] FIG. 24 illustrates an overall configuration of the content
distribution system 20. The content distribution system 20 includes: a
content management server 400; a content-using device 500; and the
communication path 300 between the content management server 400 and the
content-using device 500.

[0362] Note that in embodiment 3, constituent elements provided with the
same reference signs as in embodiment 2 indicate the same constituent
elements as those in embodiment 2.

[0363] Further, similar as in embodiment 2, the content distribution
system 20 may include two or more content management servers and two or
more content-using devices. When multiple content management servers and
multiple content-using devices are included in the content distribution
system 20, the content management servers and the content-using devices
may be interconnected via a network.

[0364] 3.2 Configuration of Content Management Server 400

[0365] FIG. 24 also illustrates a configuration of the content management
server 400. The content management server 400 includes: a reception unit
401; an invalidation instruction transmission unit 402; an invalidation
response reception unit 403; and a display unit 404, in addition to the
constituent elements included in the content management server 100
pertaining to embodiment 2. Since the constituent elements of the content
management server 400, other than those presented above, are similar to
those in embodiment 2, description is provided in the following while
focusing on the constituent elements differing between embodiments 2 and
3.

[0366] The reception unit 401 receives a user instruction for invalidating
the use of a content by a content-using device, or that is, receives an
invalidation instruction. In the following, one example is provided of
how the reception unit 401 receives an invalidation instruction.

[0367] The display unit 404 displays, for instance, a screen 411 as
illustrated in FIG. 25. The screen 411 has an input field 412 and an
input field 413. The input field 412 is for receiving input of a
content-using device name from a user, and the input field 413 is for
receiving input of a content ID from the user. The user inputs a
content-using device name and a content ID with respect to the input
field 412 and the input field 413, respectively. The reception unit 401
receives, as an invalidation instruction, the content-using device name
and the content ID having been input. Subsequently, the reception unit
401 outputs, as the invalidation instruction, the content-using device
name and the content ID having been input to the invalidation instruction
transmission unit 402.

[0368] FIGS. 26 through 29 each indicate an example of input made with
respect to the screen 411 by the user.

[0369] FIG. 26A illustrates a screen 411a. In the screen 411a, "C1" is
input to an input field 412a, and "*" is input to an input field 413a.
"C1" in the input field 412a indicates that the user has specified a
content-using device identified by a content-using device name "C1". In
addition, "*" in the input field 413a indicates that the user has
specified, as invalidation-target contents, all contents having been
provided from the content management server 400 to the content-using
device specified in the input field 412a. That is, the screen 411a
indicates that the user has specified the content-using device "C1" and
has issued an instruction for invalidating all contents in the
content-using device "C1" that have been provided by the content
management server 400.

[0370]FIG. 27 illustrates a screen 411b. In the screen 411b, "*" is input
to an input field 412b, and "Cont1" is input to an input field 413b. "*"
in the input field 412b indicates that the user has specified all
content-using devices, rather than a specific one of the content-using
devices. "Cont1" in the input field 413b indicates that the user has
specified, as an invalidation-target content, a content "Cont1" provided
by the content management server 400. That is, the screen 411b indicates
that the user has specified the content identified by the content ID
"Cont1" and has issued an instruction for invalidating the content
identified by "Cont1" in each of the content-using devices to which the
content "Cont1" has been provided.

[0371]FIG. 28 illustrates a screen 411c. In the screen 411c, "C1" is
input to an input field 412c, and "Cont1" is input to an input field
413c. "C1" in the field 412c indicates that the user has specified the
content-using device "C1". In addition, "Cont1" in the input field 413c
indicates that the user has specified, as an invalidation-target content,
a content identified by "Cont1" having been provided from the content
management server 400 to the content-using device specified in the input
field 412c. That is, the screen 411c indicates that the user has issued
an instruction for invalidating the content identified by "Cont1" in the
content-using device "C1" to which the content "Cont1" has been provided
from the content management server 400.

[0372] The device management control unit 120 reads out, from the
content-using device list 121, an IP address corresponding to a
content-using device name specified in the invalidation instruction.
Subsequently, the invalidation instruction transmission unit 402
transmits the invalidation instruction to the IP address having read out,
or that is, to the content-using specified in the invalidation
instruction.

[0373] For instance, as illustrated in FIG. 26, when input is received of
a content-using device name "C1" and a content ID "*", the device
management control unit 120 reads out, from the content-using device list
121, an IP address "192.168.1.21" stored in association with the
content-using device name "C1". Subsequently, the invalidation
instruction transmission unit 402 transmits the invalidation instruction
to the IP address "192.168.1.21". In this case, the content-using device
"C1" at the IP address "192.168.1.21" is instructed to invalidate all
contents held thereby (i.e., the contents "Cont1" and "Cont2").

[0374] On the other hand, when input is received of a content-using device
name "*" and a content ID "Cont1" as illustrated in FIG. 27, the content
management control unit 130 reads out, from the content management list
131, a management information piece including the content ID "Cont1".
Subsequently, the content management control unit 130 extracts, from the
management information piece read out, all content-using device names
included therein. Successively, the device management control unit 120
reads out, from the content-using device list 121, an IP address stored
in association with each content-using device name extracted. The
invalidation instruction transmission unit 402 transmits the invalidation
instruction to each of the IP addresses read out. In this case, each of
the content-using devices corresponding to the IP addresses is instructed
to invalidate the content identified by the content ID "Cont1". In the
example illustrated in FIG. 27, the content management control unit 130
extracts, from the content management list 131, content-using device
names "C1" and "C2". Further, the device management control unit 120
reads out, from the content-using device list 121, the IP addresses
"192.168.1.21" and "192.168.1.22". Subsequently, the invalidation
instruction is transmitted to each of the IP addresses "192.168.1.21" and
"192.168.1.22".

[0375] Further, when input is received of a content-using device name "C1"
and a content ID "Cont1" as illustrated in FIG. 28, the content
management control unit 120 reads out, from the content management list
131, an IP address "192.168.1.21" stored in association with the
content-using device name "C1". Subsequently, the invalidation
instruction transmission unit 402 transmits the invalidation instruction
to the IP address "192.168.1.21" read out. In this case, the
content-using device corresponding to the IP address "192.168.1.21" is
instructed to invalidate the content identified by the content ID
"Cont1".

[0376] Note that upon transmission of the invalidation instruction, the
invalidation instruction transmission unit 402 may check whether the
content-using device to which the invalidation instruction is to be
transmitted is online or offline by using the offline device list 122. In
such a case, the invalidation instruction transmission unit 402 may
perform control such that the invalidation instruction is not transmitted
to content-using devices that are offline. Alternatively, the
invalidation instruction transmission unit 402 may transmit the
invalidation instruction to content-using devices that are offline, in
addition to those that are online, in a similar manner as described
above. By configuring the invalidation instruction transmission unit 402
to transmit the invalidation instruction to a content-using device even
when the content-using device is offline, invalidation processing can be
performed promptly even when a content-using device registered as being
offline in the offline device list 122 has actually transitioned from
offline to online immediately before the transmission of the invalidation
instruction.

[0377] The invalidation response reception unit 403 receives an
invalidation response from a content-using device to which the
invalidation instruction has been transmitted. When an invalidation
response is not returned from a content-using device even though the
content management server 400 has recognized the content-using device as
being online, the device management control unit 120 registers the
content-using device to the offline device list 122. In specific, as
description has been provided in embodiment 2, the device management
control unit 120 registers an offline device information piece
corresponding to the content-using device to the offline device list 122.
Further, in such a case, the content management control unit 130
registers, to the content management list 131, a scheduled expiration
time with respect to the content-using device.

[0378] In contrast, when an invalidation response is returned from a
content-using device that has been recognized by the content management
server 400 as being offline, the device management control unit 120
unregisters the content-using device from the offline device list 122. In
specific, the device management control unit 120 deletes an offline
device information piece corresponding to the content-using device from
the offline device list 122. Further, in such a case, the content
management control unit 130 deletes a scheduled expiration time set with
respect to the content-using device from the content management list 131.

[0379] The display unit 404 receives the invalidation response and
displays invalidation results. FIGS. 29 through 32 each illustrate an
example of a screen displayed by the display unit 404.

[0380] (Screen 441a)

[0381] A screen 441a as illustrated in FIG. 29 is displayed when the
invalidation instruction as illustrated in FIG. 26, which is for
invalidating all contents held by the content-using device "C1", has been
transmitted. The screen 441a includes a message 442. The message 442
indicates that the content-using device "C1" is online and (that the
contents identified by the respective content names "Cont1" and "Cont2"
have been immediately invalidated.

[0382] (Screen 441b)

[0383] A screen 441b as illustrated in FIG. 30 is displayed when the
invalidation instruction as illustrated in FIG. 26, for invalidating all
contents held by the content-using device "C1", has been transmitted, and
further, when the content-using device "C1" is offline. The screen 441b
includes a message 443 indicating that the content-using device "C1" is
currently offline. In this case, the content management list 131
illustrated in FIG. 8 is referred to, and a scheduled expiration time set
with respect to each content being used by the content-using device "C1"
is read out. That is, the scheduled expiration times corresponding to the
contents identified by the content names of "Cont1" and "Cont2" are read
out. As such, the message 443 includes, in association with content
names, scheduled expiration times 443a read out.

[0384] (Screen 441c)

[0385] A screen 441c as illustrated in FIG. 31 is displayed when both of
the following conditions (i) and (ii) are satisfied.

[0386] (i) As illustrated in FIG. 27, an invalidation instruction is
issued for invalidating the content identified by the content name
"Cont1" in each content-using device.

[0387] (ii) Each content-using device is online.

[0388] The screen 441c includes a message 444 indicating that the
invalidation-target content has been invalidated. In addition, the
message 444 includes content-using device names 444a indicating the
content-using devices that have been using the corresponding content. The
content-using device names indicating the content-using devices that have
been using the corresponding content are acquired by referring to the
content management list 131.

[0389] (Screen 441d)

[0390] A screen 441d as illustrated in FIG. 32 is displayed when both of
the following conditions (i) and (ii) are satisfied.

[0391] (i) As illustrated in FIG. 27, an invalidation instruction is
issued for invalidating the content identified by the content name
"Cont1" in each content-using device.

[0392] (ii) Only the content-using device "C1" is offline and the rest of
the content-using devices are online.

[0393] The screen 441d includes a message 445 indicating that the
corresponding content has been invalidated in the content-using devices
that are online. In addition, the message 445 also includes a time point
445b indicating a time point at which the corresponding content is
scheduled to be invalidated in the content-using device that is offline.
Further, the message 445 includes content-using device names 445a
indicating the content-using devices that have been using the
corresponding content. The content-using device names of the
content-using devices that have been using the corresponding content are
acquired by referring to the content management list 131. Further, the
time point at which the corresponding content is scheduled to be
invalidated in the content-using device that is offline is acquired by
referring to a scheduled expiration time set in the content management
list 131 with respect to the content-using device that is offline.

[0394] In the above, the display unit 404 receives the invalidation
response and displays the invalidation results. However, the present
embodiment is not limited to this. That is, a modification may be made as
follows.

[0395] After having transmitted the invalidation instruction to a
content-using device and before receiving the invalidation response from
the content-using device, the device management control unit 120 may
refer to the offline device list 122. The device management control unit
120 thus determines whether or not the device name of the content-using
device is included in the offline device list 122. When the device name
of the content-using device is not included in the offline device list
122, the device management control unit 120 determines that the
content-using device is online. When the content-using device to which
the invalidation instruction has been transmitted is online, the display
unit 404 displays a message indicating that invalidation will be
immediately performed by the content-using device.

[0396] Alternatively, after having transmitted the invalidation
instruction to a content-using device and before receiving the
invalidation response from the content-using device, the content
management control unit 130 may refer to the content management list 131.
The content management control unit 130 thus determines whether or not a
scheduled expiration time is set with respect to the content-using
device. When a scheduled expiration time is set with respect to the
content-using device, the content management control unit 130 determines
that the content-using device is offline. When the content-using device
to which the invalidation instruction has been transmitted is offline,
the display unit 404 displays a scheduled expiration time set with
respect to the content-using device.

[0397] In addition, (i) when, in response to the invalidation response
transmitted to a content-using device, the invalidation response is
received from the content-using device or (ii) when, in response to the
invalidation response transmitted to a content-using device, an
invalidation response is not received within a predetermined interval
from the content-using device, and further, such a response to the
invalidation instruction having been transmitted contradicts with the
state managed by the content management server 400, the offline device
list 122 or the content management list 131 may be updated. In addition,
the invalidation results displayed may be updated. The following
describes specific examples of the above-described cases of
contradiction.

[0398] (A) when an Invalidation Response is Received

[0399] When the invalidation response is received from a content-using
device whose name is included in the offline device list 122 as an
offline device name, the reception of the invalidation response
contradicts with the corresponding offline device information piece
stored in the offline device list 122.

[0400] Further, when the invalidation response is received from a
content-using device whose name is included in the content management
list 131 as a content-using device name but when a scheduled expiration
time is stored in association with the content-using device name, the
reception of the invalidation response contradicts with the corresponding
management information piece stored in the content management list 131.

[0401] (B) when an Invalidation Response is not Received within a
Predetermined Interval

[0402] When the invalidation response is not received from a content-using
device whose name is not included in the offline device list 122 as an
offline device name, the non-reception of the invalidation response
contradicts with the corresponding offline device information piece
stored in the offline device list 122.

[0403] When the invalidation response is not received from a content-using
device whose name is included in the content management list 131 as a
content-using device name but when a scheduled expiration time is not
stored in association with the content-using device name, the
non-reception of the invalidation response contradicts with the
corresponding management information piece stored in the content
management list 131.

[0404] For instance, when the invalidation response is not returned from a
content-using device in a case where the content-using device is
recognized by the content management server 400 as being online and
display is being performed that the invalidation by the content-using
device is to be performed immediately, it can be assumed that the
content-using device has transitioned from online to offline at or
immediately before the timing at which the determination is made that the
invalidation instruction has not been returned thereto. In such a case,
the device management control unit 120 registers the content-using device
to the offline device list 122 by adding an offline device information
piece corresponding to the content-using device. Further, in such a case,
the content management control unit 130 performs, in the content
management list 131, setting of a scheduled expiration time and the like
with respect to content-using device. In addition, the display unit 404
displays the scheduled expiration time set with respect to the
content-using device.

[0405] In contrast, when the invalidation response is received from a
content-using device in a case where the content-using device is
recognized by the content management server 400 as being offline and
display is being performed of a period of validity set with respect to
the content-using device, it can be assumed that the given content-using
device has transitioned from offline to online at or immediately before
the timing at which the invalidation response has been returned thereto.
In such a case, the device management control unit 120 deletes, from the
offline device list 122, an offline device information piece including
the name of the content-using device. Further, in such a case, the
content management control unit 130 deletes, from the content management
list 131, a scheduled expiration time corresponding to the content-using
device. In addition, the display unit 404 displays a message indicating
that the invalidation by the content-using device has been performed
immediately.

[0406] 3.3 Configuration of Content-Using Device 500

[0407] FIG. 24 illustrates a configuration of a content-using device 500.
The content-using device 500 includes: an invalidation instruction
reception unit 501; and an invalidation response transmission unit 502,
in addition to the constituent elements included in the content-using
device 200 pertaining to embodiment 2. Since the constituent elements of
the content-using device 500, other than those presented above, are
similar to those in embodiment 2, description is provided in the
following while focusing on the constituent elements differing between
embodiments 2 and 3.

[0408] The invalidation instruction reception unit 501 receives an
invalidation instruction from the content management server 400 and
outputs the invalidation instruction received to the content management
control unit 221.

[0409] The content management control unit 221 receives the invalidation
instruction from the invalidation instruction reception unit 501. When
receiving the invalidation instruction, the content management control
unit 221 extracts a content ID from the invalidation instruction and
reads out, from the content management list 222, a content management
information piece including the content ID extracted. Subsequently, the
content management control unit 221 invalidates a content identified by
the content ID included in the content management information piece read
out.

[0410] Here, the content management control unit reads out, from the
content management list 222, a content management information piece
including the content ID extracted from the invalidation instruction so
as to check whether or not a content identified by the content ID
included in the invalidation instruction is held by the content-using
device 500.

[0411] The content management control unit 221 invalidates the content by
deleting the content in the content storage unit 224. When the
invalidation of the content is completed, the content management control
unit 221 generates an invalidation response indicating that the
invalidation of the content has been completed, and outputs the
invalidation response generated to the invalidation response transmission
unit 502.

[0412] Here, it should be noted that the invalidation of an
invalidation-target content is not limited to being performed in the
above-described manner. That is, the invalidation of an
invalidation-target content may be performed as described in the
following.

[0413] When the invalidation-target content is encrypted, the content
management control unit 221 may perform the invalidation of the content
by deleting a key used for decrypting the content.

[0414] Alternatively, the content management control unit 221 may output,
to the content usage control unit 223, the invalidation instruction along
with the content ID identifying the invalidation-target content. The
content usage control unit 223, when receiving the invalidation
instruction along with the content ID, may prohibit the use of the
content identified by the content ID received. The invalidation of an
invalidation-target content may be performed in such a manner. In such a
case, the content usage control unit 223 may be implemented as a
combination of an application program for controlling the use of a
content and a processor that operates according to instructions provided
from the application program.

[0415] Note that, when the use of a content is suddenly stopped by an
invalidation instruction pertaining to the content being received while
viewing of the content is in progress, the user viewing the content may
feel disappointed.

[0416] As such, control in such a case may be performed such that the use
(viewing) of the content currently under progress is continued and the
stopping of the use of the content is performed when a page subsequent to
the currently-displayed page in the content is displayed.

[0417] For instance, when the invalidation-target content is a musical
content (i.e., a song) and an invalidation instruction for invalidating
the song is received while the song is being played back, playback may be
continued until the end of the song. Subsequently, following the
termination of the playback of the song, the invalidation of the song may
be performed.

[0418] For instance, when the invalidation-target content is a still image
and an invalidation instruction for invalidating the still image is
received while the still image is being displayed, the still image may be
continuously displayed until the user terminates the display of the still
image. Subsequently, when the display of the still image is terminated by
a user operation being made, the invalidation of the still image may be
performed.

[0419] For instance, when the invalidation-target content is a moving
image composed of a plurality of scenes and an invalidation instruction
for invalidating the moving image is received while the moving image is
being played back, playback of the moving image may be continued until
the playback of a current scene finishes. Subsequently, when the playback
of the current scene is finished and the playback of the moving image is
stopped, the invalidation of the moving image may be performed.

[0420] In addition, the use of an invalidation-target content may be
stopped at a timing when an application program for viewing the content
is launched once again after being terminated once. In such a case, after
invalidation of the content is performed, a notification may be made to
the user indicating that the content has been invalidated so as to ensure
user convenience.

[0421] The invalidation response transmission unit 502 receives, from the
content management control unit 221, the invalidation response indicating
that the invalidation of the content has been completed. When receiving
the invalidation response, the invalidation response transmission unit
502 transmits the invalidation response received to the content
management server 400.

[0422] 3.4 Operations of Content Distribution System 20

[0423] In the following, description is provided on operations of the
content distribution system 20.

[0424] (1) Operations of Content Management Server 400

[0425] In the following, description is provided on operations of the
content management server 400, with reference to the sequence diagram
illustrated in FIG. 33.

[0426] The display unit 404 displays the screen 411, which is for
receiving an invalidation instruction (Step S361). Subsequently, the
reception unit 401 receives input of a content-using device name and a
content ID (Step S362). The reception unit 401 outputs the invalidation
instruction, which includes the content-using device name and the content
ID, to the invalidation instruction transmission unit 402 (Step S363).

[0428] When the content-using device specified is online ("NO" in Step
S364), the device management control unit 120 acquires an IP address
corresponding to the content-using device from the content-using device
list 121. The device management control unit 120 outputs the IP address
acquired to the invalidation instruction transmission unit 402 (Step
S365).

[0429] The invalidation instruction transmission unit 402 outputs the
invalidation instruction received to the IP address received (Step S367).
As such, the invalidation instruction is transmitted to the content-using
device specified.

[0430] When the invalidation response reception unit 403 does not receive
an invalidation response from the content-using device within a
predetermined interval ("YES" in Step S368), the device management
control unit 120 writes, to the offline device list 122, an offline
device information piece corresponding to the content-using device (Step
S372). In specific, the offline device information piece includes a
content-using device name indicating the content-using device as the
offline device name and the current time point as the offline detection
time (Step S372). In addition, the content management control unit 130
performs the calculation of: scheduled expiration time=detection
time+relative validity duration. Subsequently, the content management
control unit 130 writes, to the content management list 131, the
scheduled expiration time calculated, in association with the content ID
and the content-using device name (Step S373).

[0433] When the content-using device is online ("YES" in Step S374), the
device management control unit 120 deletes, from the offline device list
122, an offline device information piece including a content-using device
name indicating the content-using device as an offline device name (Step
S375). In addition, the content management control unit 130 deletes, from
the content management list 131, a scheduled expiration time (Step S376).
Here, the scheduled expiration time corresponds to the content ID and the
content-using device name indicating the content-using device.

[0434] (2) Operations of Content-Using Device 500

[0435] In the following, description is provided on operations of the
content-using device 500, with reference to the sequence diagram
illustrated in FIG. 34.

[0440] In the following, description is provided on an example of the
invalidation instruction in the content distribution system 20, with
reference to FIGS. 35 through 38.

[0441] FIGS. 35, 36, 37, and 38 respectively illustrate a configuration of
content distribution systems 20a, 20b, 20c, and 20d, which are examples
of the content distribution system 20. In the examples illustrated in
FIGS. 35 through 38, each of the content distribution systems 20a, 20b,
20c, and 20d includes two content management servers and three
content-using devices. More specifically, each of the content
distribution systems 20a through 20d includes: a content management
server 400a (also referred to as a "content management server S1"); a
content management server 400b (also referred to as a "content management
server S2"); a content-using device 500a (also referred to as a
"content-using device C1"); a content-using device 500b (also referred to
as a "content-using device C2"); and a content-using device 500c (also
referred to as a "content-using device C3").

[0442] In each of the content distribution systems 20a, 20b, 20c, and 20d,
the content management server 400a provides a content identified by a
content name "Cont1" and a content identified by a content name "Cont2".
The content management server 400b provides a content identified by a
content name "Cont3".

[0443] The content-using device 500a is provided, by the content
management server 400a, with the contents "Cont1" and "Cont2". The
content-using device 500a is also provided, by the content management
server 400b, with the content "Cont3".

[0444] The content-using device 500b is provided, by the content
management server 400a, with the content "Cont1".

[0445] The content-using device 500c is provided, by the content
management server 400a, with contents "Cont1" and "Cont2".

[0446] (a) A Case where, Among Contents Held by One Content-Using Device
that is Online, Each Content Provided from One Content Management Server
is Invalidated

[0447]FIG. 35 illustrates a case where, among contents held by the
content-using device 500a, each content provided from the content
management server 400a is invalidated in accordance with an invalidation
instruction from the content management server 400a. The reception of the
invalidation instruction by the content management server 400a is
performed as illustrated in FIG. 26. In addition, in the content
distribution system 20a, the content-using device 500a is online.

[0448] The content management server 400a acquires, from the content-using
device list 121, an IP address corresponding to the content-using device
500a. Subsequently, the content management server 400a outputs an
invalidation instruction 451 to the IP address acquired. The invalidation
instruction 451 is an instruction for instructing the content-using
device 500a to invalidate, among contents held by the content-using
device 500a, each content provided from the content management server
400a.

[0449] When receiving the invalidation instruction 451, the content-using
device 500a reads out, from the content management list 222 illustrated
in FIG. 12, a content management information piece including a content
management server name "S1". Subsequently, the content-using device 500a
extracts contents IDs "Cont1" and "Cont2" from the content management
information piece read out. As such, the content-using device 500a
specifies contents identified by the content IDs "Cont1" and "Cont2" as
being the invalidation-target contents indicated by the invalidation
instruction 451. Subsequently, the content-using device 500a invalidates
the contents specified. Following the invalidation of the contents, the
content-using device 500a returns an invalidation response 452 indicating
the invalidation results to the content management server 400a.

[0451] (b) A Case where, Among Contents Held by One Content-Using Device
that is Offline, Each Content Provided from One Content Management Server
is Invalidated

[0452]FIG. 36 illustrates a case where, among contents held by the
content-using device 500a, each content provided from the content
management server 400a is invalidated in accordance with an invalidation
instruction from the content management server 400a. The reception of the
invalidation instruction by the content management server 400a is
performed as illustrated in FIG. 26. In addition, in the content
distribution system 20b, the content-using device 500a is offline.

[0453] The content management server 400a acquires, from the content-using
device list 121, an IP address corresponding to the content-using device
500a. Subsequently, the content management server 400a outputs an
invalidation instruction 453 to the IP address acquired. The invalidation
instruction 453 is an instruction for instructing the content-using
device 500a to invalidate, among contents held by the content-using
device 500a, each content provided from the content management server
400a.

[0454] In this case, since the content-using device 500a is offline, the
content management server 400a does not receive a response from the
content-using device 500a in response to the invalidation instruction
453. As such, after elapse of a predetermined interval, the content
management server 400a determines that the content-using device 500a is
offline. Subsequently, the content management server 400a displays, for
instance, the screen 441b illustrated in FIG. 30 by referring to the
content management list 131 illustrated in FIG. 8.

[0455] (c) A Case where One Content Similarly Held by Multiple
Content-Using Devices that are Offline is Invalidated

[0456]FIG. 37 illustrates a case where a content identified by a content
ID "Cont1", which is similarly held by the content-using devices 500a,
500b, and 500c, is invalidated in accordance with an invalidation
instruction from the content management server 400a. The reception of the
invalidation instruction by the content management server 400a is
performed as illustrated in FIG. 27. In addition, in the content
distribution system 20c, each of the content-using devices 500a, 500b,
and 500c is online.

[0457] In a similar manner as described above, the content management
server 400a respectively outputs invalidation instructions 454, 455, and
456 to the IP addresses corresponding to the content-using devices 500a,
500b, and 500c. Each of the invalidation instructions 454, 455, and 456
is an instruction for instructing the corresponding one of the
content-using devices 500a, 500b, and 500c to invalidate, among contents
held by the corresponding one of the content-using devices 500a, 500b,
and 500c, a content identified by the content ID "Cont1".

[0458] Each of the content-using devices 500a, 500b, and 500c, when
receiving the corresponding one of the invalidation instructions 454,
455, and 456, invalidates the content identified by the content ID
"Cont1". Subsequently, the content-using devices 500a, 500b, and 500c
respectively return invalidation responses 457, 458, and 459, which
indicate the completion of the invalidation, to the content management
server 400a. The content management server 400a, when receiving the
invalidation responses 457, 458, and 459, displays, for instance, the
screen 441c illustrated in FIG. 31.

[0459] (d) A Case where a Content Similarly Held by Multiple Content-Using
Devices, Some of which being Online and the Rest being Offline, is
Invalidated.

[0460]FIG. 38 illustrates a case where a content identified by a content
ID "Cont1", which is similarly held by the content-using devices 500a,
500b, and 500c, is invalidated in accordance with an invalidation
instruction from the content management server 400a. The reception of the
invalidation instruction by the content management server 400a is
performed as illustrated in FIG. 27. In addition, in the content
distribution system 20d, the content-using device 500a is online, whereas
the content-using devices 500b and 500c are offline.

[0461] In a similar manner as described above, the content management
server 400a respectively outputs invalidation instructions 460, 461, and
462 to the IP addresses corresponding to the content-using devices 500a,
500b, and 500c. Each of the invalidation instructions 460, 461, and 462
is an instruction for instructing the corresponding one of the
content-using devices 500a, 500b, and 500c to invalidate, among contents
held by the corresponding one of the content-using devices 500a, 500b,
and 500c, a content identified by the content ID "Cont1".

[0462] In this case, since the content-using device 500a is offline, the
content management server 400a does not receive a response from the
content-using device 500a in response to the invalidation instruction
460. As such, after elapse of a predetermined interval, the content
management server 400a determines that the content-using device 500a is
offline.

[0463] In the meantime, each of the content-using devices 500b and 500c
invalidates the content identified by the content ID "Cont1".
Subsequently, the content-using devices 500b and 500c respectively return
invalidation responses 463 and 464, which indicate the completion of the
invalidation, to the content management server 400a.

[0464] Subsequently, since the content-using device 500a is offline, the
content management server 400a refers, for instance, to the content
management list 131 illustrated in FIG. 8 and reads out a scheduled
expiration time indicating the period of validity of the content
identified by the content ID "Cont1". Subsequently, the content
management server 400a displays, for instance, a screen 44d as
illustrated in FIG. 32.

[0465] Note that playback of the content identified by the content name of
"Cont1" in the content-using device 500a is automatically disabled when
the time point indicated by the scheduled expiration time is reached.
Further, when the content-using device 500a transitions from offline to
online before the scheduled expiration time is reached, the content-using
device 500a makes a notification of the transition from offline to online
to the content management server 400a. As such, the content management
server 400a need only issue an invalidation instruction once again with
respect to the content-using device 500a when such a notification
indicating the transition from offline to online is received from the
content-using device 500a.

[0466] 3.6. Effects Achieved by Embodiment 3

[0467] In embodiment 3, when a corresponding content-using device is
online when an invalidation instruction for invalidating a content is
received from a user, immediate invalidation of the content is performed
by the content-using device. On the other hand, when a corresponding
content-using device is offline when an invalidation instruction for
invalidating a content is received from a user, the user is notified of
when the content will be invalidated in the content-using device.

[0468] As such, when a user provides contents to a content-using device
corresponding to another user and later invalidates all of the contents
he/she has provided to the content-using device corresponding to the
other user due to reasons such as a change in the relationship with the
other user, the user is able to know when the invalidation of the
contents will be completed. As such, the user is able to perform the
invalidation of the contents free of concerns.

[0469] In addition, when a user desires to invalidate a content which has
been distributed to an unidentified number of content-using devices due
to he/she having made an operational mistake, the user is able to know
the total number of content-using devices to which the content has been
distributed. Further, in such a case, the user is able to know in how
many of the content-using devices the content will be immediately
invalidated online. Further in addition, the user is able to know when a
specific content will be invalidated from all existing content-using
devices, including offline devices, to which the content has been
provided. As such, the user is able to perform the invalidation of
contents free of concerns.

4. Embodiment 4

[0470] In the following, description is provided on a content distribution
system 30 pertaining to embodiment 4 of the present invention, with
reference to the accompanying drawings.

[0471] The content distribution system 30 differs from the content
distribution system 10 in that a content-using device in the content
distribution system 30 performs polling at regular intervals with respect
to a content management server in the content distribution system 30. Due
to this, the content management server is able to determine only the
content-using device performing polling with respect to the content
management server as being online while the other content-using devices,
which do not perform polling, are determined as being offline.

[0472] 4.1 Overall Configuration of Content Distribution System 30

[0473]FIG. 39 illustrates an overall configuration of the content
distribution system 30. The content distribution system 30 includes: a
content management server 600; a content-using device 700; and the
communication path 300 between the content management server 600 and the
content-using device 700.

[0474] Note that in the content distribution system 30, constituent
elements provided with the same reference signs as in the content
distribution system 10 indicate the same constituent elements as those in
the content distribution system 10.

[0475] Further, similar as the content distribution system 10, the content
distribution system 30 may include two or more content management servers
and two or more content-using devices. Further, when multiple content
management servers and multiple content-using devices are included in the
content distribution system 20, the content management servers and the
content-using devices may be interconnected via a network.

[0481] The polling reception unit 610 receives a polling command from the
content-using device 700. The polling reception unit 610 outputs
information included in the polling command received to the online
control determination unit 611.

[0482] (Online Control Determination Unit 611)

[0483] The online control determination unit 611 determines a
content-using device that is online according to the information included
in the polling command (e.g., an IP address) received from the polling
reception unit 610. Further, the online control determination unit 611
instructs the polling Ack transmission unit 612 to transmit a polling
Ack.

[0484] The online control determination unit 611 transmits information
pertaining to the content-using device having transmitted the polling
command, along with the time point at which the polling command has been
received, to the device management unit 602. Here, the information
pertaining to the content-using device is, for instance, an IP address.

[0485] (Polling Ack Transmission Unit 612)

[0486] The polling Ack transmission unit 612, when receiving the
instruction for transmitting a polling Ack from the online control
determination unit 611, generates a polling Ack. Subsequently, the
polling Ack transmission unit 612 transmits the polling Ack to the
content-using device from which the polling command has been transmitted.

[0490]FIG. 42 is a chart indicating one example of a data configuration
of the content-using device list 621. The content-using device list 621
stores, in an associated state, each content-using device receiving a
content from the content management server 600 and a corresponding
connection destination. Here, the connection destination of a
content-using device is, for instance, an IP address.

[0491] In specific, the content-using device list 621 is provided with
areas for storing multiple content-using device information pieces. Each
content-using device information piece includes a content-using device
name and an IP address. A content-using device name is a name identifying
a content-using device, and an IP address indicates a location on an IP
network at which the content-using device is located.

[0492] (Online Device List 622)

[0493]FIG. 43 is a chart indicating one example of a data configuration
of the online device list 622. The online device list 622 is provided
with areas for storing multiple online device information pieces. Each
online device information piece includes an online device name and a
final access time. An online device name is a name identifying a
content-using device determined as being online. A final access time
indicates a time point at which the content-using device most recently
accessed the content management server 600. More specifically, a final
access time includes indication of the month, the day, and the time
corresponding to the last time the content-using device accessed the
content management server 600.

[0494] The online device list 622 includes, for instance, an online device
information piece including "C1" in an online device name field 624 and
"1/21, 23:00" in a final access time field 625. This online device
information piece indicates that the content management server 600 most
recently received a polling command from the content-using device
indicated by "C1" in the online device name field 624 at 23:00, January
21st as indicated in the final access time field 625. The storing of
the final access time and the content-using device name as the online
device name in the online device list 622 was performed at 23:00, January
21st. The indication in the final access time field 625 indicates
the time point at which the content-using device "C1" most recently
accessed the content management server 600. In other words, according to
the online device list 622, the content-using device "C1" has not
accessed the content management server 600 since 23:00, January
21st.

[0495] (Device Management Control Unit 620)

[0496] The device management control unit 620 controls the writing, the
reading out, and the updating of content-using device information with
respect to the content-using device list 621. The device management
control unit 620 also controls the writing, the reading out, and the
updating of online device information with respect to the online device
list 622. The device management control unit 620 receives, from the
online detection unit 601, information pertaining to a content-using
device (e.g., an IP address of the content-using device), and reads out,
from the content-using device list 621, a corresponding content-using
device name.

[0497] In addition, the device management control unit 620, when updating
the online device list 622, transmits an updated online device name and
an updated final access time to the content management unit 603.

[0501]FIG. 45 is a chart indicating one example of a data configuration
of the content management list 631.

[0502] The content management list 631 is provided with areas for storing
multiple management information pieces. Each management information piece
includes: one content ID; one validity duration; and zero, one, or
multiple usage device information pieces. That is, a management
information piece includes either (i) a combination of one content ID and
one validity duration or (ii) a combination of one content ID, one
validity duration, and one or more usage device information pieces. A
management information piece including a combination of one content ID
and one validity duration indicates an initial state. When a management
information piece is in the initial state, one or more usage device
information pieces may be added thereto. Further, when a management
information piece includes one or more usage device information pieces,
one or more usage device information pieces may further be added to the
management information piece.

[0503] A content ID is identification information uniquely identifying a
content. A validity duration is in correspondence with a content ID and
indicates a time period (a duration) from the point at which the content
identified by the content ID is distributed, during which the use of the
content by content-using devices is permitted. A content-using device
name identifies a content-using device. The content-using device
identified by the content-using device name uses the content identified
by the corresponding content ID. A scheduled expiration time is
calculated from the point at which the corresponding content has been
distributed to the corresponding content-using device and indicates a
time point at which the period of validity of use of the content by the
content-using device expires.

[0504] (Content Management Control Unit 630)

[0505] The content management control unit 630 controls the writing, the
reading out, and the updating of management information with respect to
the content management list 631.

[0506] In specific, when a content is provided to a content-using device,
the content management control unit 630 receives a content ID identifying
the content, a content-using device name identifying the content-using
device, and a distribution time at which the content has been distributed
to the content-using device. Subsequently, the content management control
unit 630 uses the content ID identifying the distributed content and
thereby reads out, from the content management list 631, a management
information piece including the content ID. Subsequently, the content
management control unit 630 extracts a validity duration from the
management information piece read out. Subsequently, the content
management control unit 630 sets a scheduled expiration time by adding
the validity duration to the distribution time.

Scheduled Expiration Time=Distribution Time+Validity Duration

[0507] Subsequently, the content management control unit 630 writes and
thereby adds a usage device information piece including the content-using
device name and the scheduled expiration time to the management
information piece read out from the content management list 631.

[0508] In addition, when receiving a content-using device name and a final
access time from the device management control unit 620, the content
management control unit 630 updates the scheduled expiration time set
with respect to the content-using device identified by the content-using
device name received by adding the validity duration to the final access
time.

[0509] More specifically, the content management control unit 630 reads
out, from the content management list 631, a management information piece
including a content-using device name of a content-using device that is
online. Subsequently, the content management control unit 630 extracts a
validity duration from the management information piece read out, and
extracts a usage device information piece including the content-using
device name from the management information piece read out. Subsequently,
the content management control unit 630 adds the validity duration
extracted to the final access time received and sets the time obtained as
a result of the addition as the scheduled expiration time.

Scheduled Expiration Time=Final Access Time+Validity Duration

[0510] Subsequently, the content management control unit 630 overwrites
the scheduled expiration time included in the usage device information
piece having been extracted by using the scheduled expiration time
obtained as a result of the calculation. Subsequently, the content
management control unit 630 writes back the usage device information
piece including an overwritten scheduled expiration time to the content
management list 631.

[0511] (Content Management List 631)

[0512] The content management list 631 includes a management information
piece 639 as illustrated in FIG. 45. The management information piece 639
includes: "Cont1" in a content ID field 633; "24H" in a validity duration
field 634; "C1" in a content-using device name field 635; "1/21, 00:00"
in a scheduled expiration time field 636; "C2" in a content-using device
name field 637; and "1/21, 00:00" in a scheduled expiration time field
638.

[0513] The management information piece 639 indicates, for instance, that
the content identified by "Cont1" in the content ID field 633 has been
distributed at 00:00, January 20th to the content-using devices
identified by "C1" in the content-using device name field 635 and "C2" in
the content-using device name field 637. Further, the management
information piece 639 indicates that "24H" is the validity duration of
the content identified by "Cont1" in the content ID field 633. As such,
the scheduled expiration time of the content "Cont1" with respect to each
of the content-using devices identified by "C1" in the content-using
device name field 635 and "C2" in the content-using device name field 637
is calculated as "1/21, 00:00" as indicated in the scheduled expiration
time fields 636 and 638, which is later by "24H" in the validity duration
field 634 than the distribution time "1/20, 00:00".

[0514] (Content Management List 631a)

[0515]FIG. 46 is a chart indicating one example of a data configuration
of a content management list 631a, which is another example of the
content management list 631.

[0516] The content management list 631a includes a management information
piece 639a and a management information piece 646a as illustrated in FIG.
46. The management information piece 639a includes: "Cont1" in the
content ID field 633; "24H" in the validity duration field 634; "C1" in
the content-using device name field 635; "1/21, 23:00" in a scheduled
expiration time field 636a; "C2" in the content-using device name field
637; and "1/21, 00:00" in the scheduled expiration time field 638. The
management information piece 646a includes: "Cont2" in a content ID field
640; "48H" in a validity duration field 641; "C1" in a content-using
device name field 642; "1/22, 23:00" in a scheduled expiration time field
643a; "C3" in a content-using device name field 644; and "1/22, 00:00" in
a scheduled expiration time field 645.

[0517] For instance, when an online device name "C1" and a final access
time "1/20, 23:00" are received from the device management control unit
620, first, the management information piece 639 including the device
name "C1" as the content-using device name is read out from the content
management list 631, and then, extraction is performed of "24H" in the
validity duration field 634 in the management information piece 639 and
the usage device information piece including the device name "C1" as the
content-using device name. Subsequently, the time point "1/21, 23:00" is
calculated by adding "24H" in the validity duration field 634 extracted
to the final access time "1/20, 23:00". Subsequently, overwriting is
performed of "1/21, 00:00" in the scheduled expiration time field 636 in
the usage device information piece extracted by setting the time point
"1/21, 23:00" obtained as a result of the calculation as the scheduled
expiration time. Subsequently, the usage device information piece
including the overwritten scheduled expiration time of "1/21, 23:00" is
written back to the management information piece 639 in the content
management list 631. As such, the management information piece 639a
includes "1/21, 23:00" in the scheduled expiration time field 636a as in
the content management list 631a illustrated in FIG. 46.

[0518] In addition, similar as in the above, the management information
piece 646 including the device name "C1" as the content-using device name
is read out from the content management list 631. Then, extraction is
performed of "48H" in the validity duration field 641 in the management
information piece 646 and the usage device information piece including
the device name "C1" as the content-using device name. Subsequently, the
time point "1/22, 23:00" is calculated by adding "48H" in the validity
duration field 641 extracted to the final access time "1/20, 23:00".
Subsequently, overwriting is performed of "1/22, 00:00" in the scheduled
expiration time field 643 in the usage device information piece extracted
by setting the time point "1/22, 23:00" obtained as a result of the
calculation as the scheduled expiration time. Subsequently, the usage
device information piece including the overwritten scheduled expiration
time of "1/22, 23:00" is written back to the management information piece
646 in the content management list 631. As such, the management
information piece 646a includes "1/22, 23:00" in the scheduled expiration
time field 643a as in the content management list 631a illustrated in
FIG. 46.

[0519] The updating of the content management list 631 illustrated in FIG.
45 is performed in such a manner as described above, whereby the content
management list 631a illustrated in FIG. 46 is obtained. Compared with
the content management list 631, the content management list 631a
includes updated scheduled expiration times in the scheduled expiration
time fields 636a and 643a.

[0520] 4.3 Content-Using Device 700

[0521]FIG. 39 illustrates a configuration of the content-using device
700. The content-using device 700 includes: an online notification unit
701; a content control unit 702; and a time measurement unit 703.

[0525] The polling transmission unit 701 receives a polling transmission
instruction and information pertaining to an address to which a polling
command is to be transmitted from the online control determination unit
711. When receiving the polling transmission instruction and the
information pertaining to the address, the polling transmission unit 701
transmits a polling command to the content management server 600.
Following the transmission of the polling command, the polling
transmission unit 701 transmits information pertaining to the
transmission destination and a transmission time at which the polling
command has been transmitted to the polling Ack reception unit 712.

[0526] (Online Control Determination Unit 711)

[0527] The online control determination unit 711 determines whether the
content-using device 700 is online or offline. For instance, the online
control determination unit 711 determines whether the content-using
device 700 is online or offline by determining whether or not a polling
Ack is received from the content management server 600 in response to a
polling command having been transmitted. That is, the online control
determination unit 711 determines that the content-using device 700 is
online when a polling Ack is received from the content management server
600. On the other hand, the online control determination unit 711
determines that the content-using device 700 is offline when a polling
Ack is not received from the content management server 600.

[0528] Alternatively, the online control determination unit 711 may
determine whether the content-using device 700 is online or offline by
determining whether or not a communication module in the content-using
device 700 is activated or not.

[0529] Alternatively, when the content-using device 700 performs wireless
communication, the online control determination unit 711 may determine
whether or not the content-using device 700 is online or offline by
determining whether or not the content-using device 700 is located within
a distance from an access point within which radio signals transmitted
from the content-using device 700 reach the access point.

[0530] In addition, the online control determination 711 may determine
that the content-using device 700 is not online when a transmission error
is received from a router when performing polling.

[0531] When determining that the content-using device 700 is online, the
online control determination unit 711 transmits, to the polling
transmission unit 710, the polling transmission instruction along with
the information pertaining to the address of the content management
server 600. In addition, the content-using device 700, when receiving a
notification of a scheduled expiration time of a content from the content
control unit 702, outputs a polling transmission instruction to the
polling transmission unit 710 before the scheduled expiration time is
reached. The online control determination unit 711 receives, from the
polling Ack reception unit 712, a polling Ack transmitted from the
content management server 600. Subsequently, the online control
determination unit 711 outputs, to the content control unit 702, a
content management server name and a transmission time indicating the
time point at which the polling has been performed.

[0532] (Polling Ack Reception Unit 712)

[0533] The polling Ack reception unit 712 receives a polling Ack from the
content management server 600. By receiving the polling Ack from the
content management server 600, the polling Ack reception unit 712
determines that a notification has been made to the content management
server 600 that the content-using device 700 is online. Subsequently, the
polling Ack reception unit 712 notifies the online control determination
unit 711 that a notification has been made to the content management
server 600 that the content-using device 700 is online.

[0537] The content management control unit 721 manages a content stored in
the content-using device 700 by using the content management list 722,
detailed description of which is provided in the following. The content
management control unit 721 refers to a scheduled expiration time
included in the content management list 722, and when the scheduled
expiration time indicates that the use of a corresponding content is
permitted, controls the content playback unit 725 such that the use of
the corresponding content stored in the content storage unit 723 is
enabled. In contrast, when the scheduled expiration time included in the
content management list 722 has already passed, the content management
control unit 721 controls the content playback unit 725 so as to stop the
use of the corresponding content stored in the content storage unit 723.
In addition, when referring to a scheduled expiration time included in
the content management list 722, the content management control unit 721
makes a notification to the online control determination unit 711. In
addition, when receiving the content management server name and the
polling transmission time from the online control determination unit 711,
the content management control unit 721 updates a scheduled expiration
time included in the content management list 722 as described in the
following.

[0538] (Content Management List 722)

[0539] The content management list 722 is a list for managing contents
received from the content management server 600. FIG. 49 is a chart
indicating one example of a data configuration of the content management
list 722. The content management list 722 is provided with areas for
storing multiple management information pieces. Each management
information piece includes a content ID, a validity duration, a content
management server name, and a scheduled expiration time. A content ID is
identification information uniquely identifying a content. A validity
duration is in correspondence with a content ID and indicates a duration
during which the use of the content by content-using devices is
permitted. A content management server name is a name identifying a
content management server that has transmitted the corresponding content.
A scheduled expiration indicates a time point at which a period of
validity, during which the content-using device 700 is permitted to use
the content, expires.

[0541] The management information piece 731 includes: "Cont1" in a content
ID field 734; "24H" in a validity duration field 735; "S1" in a content
management server name field 736; and "1/21, 00:00" in a scheduled
expiration time field 737.

[0542] The management information piece 731 indicates a situation as
follows. The content identified by "Cont1" in the content ID field 734
has been supplied from the content management server identified by "S1"
in the content management server name field 736. Further, the period
during which the content-using device 700 is permitted to use the content
"Cont1" is "24H" as indicated in the validity duration field 735. In
addition, the period during which the content-using device 700 is
permitted to use the content "Cont1" ends at "1/21, 00:00" as indicated
in the scheduled expiration time field 737. Here, "1/21, 00:00" in the
scheduled expiration time field 737 is calculated by adding "24H" in the
validity duration field 733 to a time point at which the content "Cont1"
has been received from the content management server "S1".

[0543] The management information piece 732 includes: "Cont2" in a content
ID field 738; "48H" in a validity duration field 739; "S1" in a content
management server name field 740; and "1/22, 00:00" in a scheduled
expiration time field 741. The management information piece 732 indicates
a situation as follows. The content identified by "Cont2" in the content
ID field 738 has been supplied from the content management server
identified by "S1" in the content management server name field 740.
Further, the period during which the content-using device 700 is
permitted to use the content "Cont2" is "48H" as indicated in the
validity duration field 739. In addition, the period during which the
content-using device 700 is permitted to use the content "Cont2" ends at
"1/22, 00:00" as indicated in the scheduled expiration time field 741.
Here, "1/22, 00:00" in the scheduled expiration time field 741 is
calculated by adding "48H" in the validity duration field 739 to a time
point at which the content "Cont2" has been received from the content
management server "S1".

[0544] The management information piece 733 includes: "Cont3" in a content
ID field 742; "24H" in a validity duration field 743; "S2" in a content
management server name field 744; and "1/21, 23:30" in a scheduled
expiration time field 745. Since the situation indicated by the
management information piece 733 is obvious when referring to the above,
description thereon is omitted herein.

[0545] (Content Management List 722a)

[0546]FIG. 50 is a chart indicating one example of a data configuration
of a content management list 722a, which is another example of the
content management list 722. The content management control unit 721,
when receiving a content management server name and a polling
transmission time from the online control determination unit 711, updates
a scheduled expiration time in the content management list 722.

[0547] For instance, in the example of the case indicated by the content
management list 722a illustrated in FIG. 50, the content management
control unit 721 has received a content management server name "S1" and a
polling transmission time "1/20, 23:00" from the online control
determination unit 711. In such a case, the content management control
unit 721 updates a scheduled expiration time for each content
corresponding to the content management server "S1" such that each
scheduled expiration time indicates a time point calculated by adding the
corresponding validity duration to the polling transmission time "1/20,
23:00". For instance, when taking as an example the content "Cont1",
updating of the scheduled expiration time is performed such that the
updated scheduled expiration time indicates "1/21, 23:00", which is
calculated by adding the corresponding validity duration of "24H" to the
polling transmission time "1/20, 23:00". Further, when taking as an
example the content "Cont2", updating of the scheduled expiration time is
performed such that the updated scheduled expiration time indicates
"1/22, 23:00", which is calculated by adding the corresponding validity
duration of "48H" to the polling transmission time "1/20, 23:00". As a
result, the content management list 722a illustrated in FIG. 50 includes
"1/21, 23:00" in a scheduled expiration time field 737a instead of "1/21,
00:00" in the scheduled expiration time 737 included in the content
management list 722, and includes "1/22, 23:00" in a scheduled expiration
time field 741a instead of "1/22, 00:00" in the scheduled expiration time
field 741 included in the content management list 722.

[0548] 4.4 Operations of Content Distribution System 30 (Part 1)

[0549] In the following, description is provided on operations of the
content distribution system 30.

[0550] (1) Operations of Content Management Server 600 when a Contents is
Provided to a Content-Using Device

[0551] In the following, description is provided on operations involved in
the updating of the content management list 631 by the content management
control unit 630 when a content is provided from the content management
server 600 to a content-using device, with reference to the flowchart
illustrated in FIG. 51.

[0552] When a content is provided to a content-using device, the content
management control unit 630 receives a content ID identifying the
content, a content-using device name identifying the content-using
device, and a distribution time at which the content has been distributed
(Step S501).

[0553] Subsequently, the content management control unit 630, reads out,
from the content management list 631, a management information piece
including the content ID and the content-using device name received (Step
S502). Subsequently, the content management control unit 630 extracts a
validity duration from the management information piece read out (Step
S503). Subsequently, the content management control unit 630 adds the
validity duration read out to the distribution time received, and sets
the time point obtained as a result of the calculation as a scheduled
expiration time (Step S504). Subsequently, the content management control
unit 630 generates a usage device information piece including the
content-using device name and the scheduled expiration time. Further, the
content management control unit 630 writes, to the content management
list 631, the usage device information piece so generated in association
with the content ID and the validity duration (Step S505).

[0555] In the following, description is provided on operations of the
content management server 600 when receiving a polling command from the
content-using device 700, with reference to the sequence diagram
illustrated in FIG. 52.

[0557] The online control determination unit 611 determines a
content-using device that is online by using the IP address included in
the polling command (Step S513). The online control determination unit
611 also outputs an instruction for generating a polling Ack to the
polling Ack transmission unit 612 (Step S514).

[0558] The polling Ack transmission unit 612 generates a polling Ack (Step
S515), and transmits the polling Ack generated to the content-using
device 700, from which the polling command has been received (Step S516).

[0559] Subsequently, the online control determination unit 611 outputs, to
the device management control unit 620, a reception time at which the
polling command has been received and the IP address included in the
polling command (Step S517).

[0560] The device management control unit 620 acquires, by using the
content-using device list 621, a content-using device name corresponding
to the IP address (Step S518). Subsequently, the device management
control unit 620 reads out, from the online device list 622, an online
device information piece including the content-using device name
acquired. Subsequently, the device management control unit 620 overwrites
a final access time included in the online device information piece read
out with the reception time, and writes back, to the online device list
622, the online device information piece including the overwritten final
access time (Step S519). Then, the device management control unit 620
transmits the online device name and the final access time to the content
management control unit 630 (Step S520).

[0561] The content management control unit 630, reads out, from the
content management list 631, a management information piece including the
device name received as a content-using device name (Step S521).
Subsequently, the content management control unit 630 extracts a validity
duration from the management information piece read out (Step S522).
Subsequently, the content management control unit 630 performs the
calculation of: scheduled expiration time=final access time+validity
duration (Step S523). Subsequently, the content management control unit
630 overwrites the scheduled expiration time corresponding to the
content-using device name in the management information piece read out
with the scheduled expiration time so calculated. Subsequently, the
content management control unit 630 writes back, to the content
management list 631, the management information piece including the
overwritten scheduled expiration time (Step S524).

[0563] In the following, description is provided on operations of the
content-using device 700 when outputting a polling command, with
reference to the sequence diagrams illustrated in FIGS. 53 and 54.

[0564] The online control determination unit 711 determines whether the
content-using device 700 is online (Step S531). When the content-using
device is online ("YES" in Step S532), the online control determination
unit 711 outputs a polling transmission instruction and an address to
which a polling command is to be transmitted to the polling transmission
unit 710 (Step S533). The online control determination unit 711 also
outputs a polling transmission time and the address to the content
management control unit 721 (Step S534).

[0565] The polling transmission unit 710 generates a polling command and
outputs the polling command to the address received (Step S511).

[0566] The content management control unit 721 tries to read out, from the
content management list 722, a management information piece including the
address (i.e., a specific content management server name) (Step S535).
When the reading out of the management information piece is completed
without reading being performed of the entire content management list 722
("NO" in Step S536), the content management control unit 721 extracts a
validity duration from the management information piece read out (Step
S537). Subsequently, the content management control unit 721 performs the
calculation of: scheduled expiration time=polling transmission
time+validity duration (Step S538). Subsequently, the content management
control unit 721 overwrites the scheduled expiration time included in the
management information piece read out with the scheduled expiration time
so calculated. Subsequently, the content management control unit 721
writes back, to the content management list 722, the management
information piece including the overwritten scheduled expiration time
(Step S539). Then, the content management control unit 721 returns to
Step S535 and performs processing once again from Step S535.

[0568] When the reading out of the management information piece is not
completed even when reading has been performed of the entire content
management list 722 ("YES" in Step S536), the content management control
unit 721 tries to read out, from the content management list 722, a
management information piece including the address (i.e., a specific
content management server name) (Step S561). When the reading out of the
management information piece is completed without reading being performed
of the entire content management list 722 ("NO" in Step S562), the
content management control unit 721 extracts a scheduled expiration time
from the management information piece read out (Step S563). Subsequently,
the content management control unit 721 outputs the scheduled expiration
time extracted to the online control determination unit 711 (Step S564).

[0569] The online control determination unit 711 determines whether the
current time point precedes the scheduled expiration time (Step S565).
When the current time point does not precede the scheduled expiration
time ("NO" in Step S564), the online control determination unit 711
returns to Step S562 and performs processing once again from Step S562.
When the current time point precedes the scheduled expiration time ("YES"
in Step S564), the online control determination unit 711 proceeds to the
processing following Step S532.

[0570] (4) Operations of Content-Using Device 700 when Determining Control
of a Content being Used

[0571] In the following, description is provided on operations of the
content-using device 700 when determining control of a content being
used, with reference to the sequence diagram illustrated in FIG. 55.

[0572] The content management control unit 721 reads out, from the content
management list 722, a management information piece pertaining to a
content being used (Step S571). Subsequently, the content management
control unit 721 extracts a scheduled expiration time from the management
information piece read out (Step S572). Subsequently, the content
management control unit 721 determines whether the current time point
succeeds the scheduled expiration time (Step S573). When the current time
point succeeds the scheduled expiration time ("Has passed" in Step S573),
the content management control unit 721 stops the use of the content
(Step S575). When the current time point does not succeed the scheduled
expiration time ("Has not passed" in Step S573), the content management
control unit 721 permits the use of the content (Step S574).

[0573] 4.5 Configuration of Content Distribution System 30

[0574]FIG. 56 is a diagram illustrating a configuration of a content
distribution system 30a, which is one example of the content distribution
system 30. In the example illustrated in FIG. 56, the content
distribution system 30a includes two content management servers and three
content-using devices. More specifically, the content distribution system
30a includes: a content management server 600a (also referred to as a
"content distribution server S1"); a content management server 600b (also
referred to as a "content distribution server S2"); a content-using
device 700a (also referred to as a "content-using device C1"); a
content-using device 700b (also referred to as a "content-using device
C2"); and a content-using device 700c (also referred to as a
"content-using device C3").

[0575]FIG. 56 illustrates how contents are shared between the content
management servers and the content-using devices. Further, FIG. 56 also
illustrates connections between the content management servers and the
content-using devices.

[0576] The content management server 600a provides a content identified by
a content name "Cont1" and a content identified by a content name
"Cont2". In addition, the content management server 600b provides a
content identified by a content name "Cont3".

[0577] The content-using device 700a is provided, by the content
management server 600a, with the contents "Cont1" and "Cont2". The
content-using device 700a is also provided, by the content management
server 600b, with the content "Cont3".

[0578] The content-using device 700b is provided, by the content
management server 600a, with the content "Cont1".

[0579] The content-using device 700c is provided, by the content
management server 600a, with the contents "Cont1" and "Cont2".

[0580] As such, the contents "Cont1" and "Cont2" are shared between the
content management server 600a and the content-using device 700a. That
is, the contents "Cont1" and "Cont2" possessed by the content management
server 600a are provided for use to the content-using device 700a.

[0581] Similarly, the content "Cont1" is shared between the content
management server 600a and the content-using device 700b. That is, the
content "Cont1" possessed by the content management server 600a is
provided for use to the content-using device 700b.

[0582] Further, the contents "Cont1" and "Cont2" are shared between the
content management server 600a and the content-using device 700c. That
is, the contents "Cont1" and "Cont2" possessed by the content management
server 600a are provided for use to the content-using device 700c.

[0583] In addition to the above, the content "Cont3" is shared between the
content management server 600b and the content-using device 700a. That
is, the content "Cont3" possessed by the content management server 600b
is provided for use to the content-using device 700a.

[0584] Here, the content possessed by the content management server 600b
is not used by the content-using device 700b. That is, as illustrated in
FIG. 56, the content management server 600b and the content-using device
700b are not connected with each other. The same applies to the content
management server 600b and the content-using device 700c.

[0585] 4.6 Operations of Content Distribution System 30 (Part 2)

[0586] Note that in the following, based on the configuration illustrated
in FIG. 56, description is provided on the interaction between the
content management server 600a and the content-using device 700a, with
reference to FIGS. 57 and 58.

[0587] Step 11) At 00:00, January 20th, the content management server
600a transmits, to the content-using device 700a, the contents identified
by the respective content IDs "Cont1" and "Cont2" in response to a
request made from the content-using device 700a. In addition, the content
management server S1 stores a usage device information piece
corresponding to the content-using device 700a to the content management
list 631 (Step S201). The content management list 631 at this point is as
illustrated in FIG. 45. Subsequently, at time point T11, the
content-using device 700a receives the contents "Cont1" and "Cont2" and
stores management information pieces corresponding to the contents to the
content management list 722 (Step S211). The content management list 722
at time point T11 is as illustrated in FIG. 49. Here, for instance, the
validity duration of the content "Cont1" is "24H", and hence, the
scheduled expiration time for the content "Cont1" is time point T14,
which is calculated by adding "24H" to time point T11. In other words,
the content "Cont1" is available for use from time point T11 to time
point T14.

[0588] Step 12) At 23:00, January 20th (time point T12), the
content-using device 700a transmits a polling command to the content
management server 600a (Step S212). The content management server 600a
receives the polling command from the content-using device 700a, and
generates and transmits a polling Ack within a predetermined interval
from the reception of the polling command (Step S202). The content
management server 600a, at this point, determines that the content-using
device 700a is online and updates the content management list 631 (Step
S203). The content management list 631a, which corresponds to the content
management list 631 following the update, is as illustrated in FIG. 46.
The content-using device 700a receives a polling Ack from the content
management server 600a (Step S212). By receiving the polling Ack from the
content management server 600a, the content-using device 700a determines
that a notification has been made to the content management server 600a
that the content-using device 700a is online (Step S212). The
content-using device 700a updates the content management list 722 at time
point T13 (Step S213). The content management list 722a, which
corresponds to the content management list 722 following the update, is
as illustrated in FIG. 50. Here, for instance, the validity duration of
the content "Cont1" is "24H", and hence, the scheduled expiration time
for the content "Cont1" is time point T18, which is calculated by adding
"24H" to time point T12. In other words, the content "Cont1" is available
for use from time point T12 to time point T18.

[0589] Step 13) The content-using device 700a transitions from online to
offline at 23:30, January 20th (time point T15). Even after
transitioning from online to offline, the content-using device 700a is
able to continue the use of the content "Cont1" since the scheduled
expiration time of the content "Cont1" is "1/21, 23:00". Subsequently,
the content-using device 700a transitions to online once again as the
scheduled expiration time "1/21, 23:00" of the content "Cont1"
approaches. In the example illustrated in FIG. 58, the content-using
device 700a transitions from offline to online at 22:00, January
21st, which is one hour before the scheduled expiration time. At
time point T16 immediately following 22:00, January 21st, which is
the time point at which the content-using device 700a transitions from
offline to online, the content-using device 700a transmits a polling
command to the content management server 600a (Step S214). The content
management server 600a receives the polling Ack from the content-using
device 700a (Step S204). Then, within a predetermined interval from the
reception of the polling command, the content management server 600a
transmits a polling Ack to the content-using device 700a (Step S204). The
content management server 600a, at this point, determines that the
content-using device 700a is online and updates the content management
list 631a (Step S205). A content management list 631b, which corresponds
to the content management list 631a following the update, is as
illustrated in FIG. 59. In the content management list 631b, which
corresponds to the content management list 631a following the update,
"1/22, 22:00" is set in a scheduled expiration time field 636b, and
"1/23, 22:00" is set in a scheduled expiration time field 643b. The
content-using device 700a receives a polling Ack from the content
management server 600a (Step S214). By receiving the polling Ack from the
content management server 600a, the content-using device 700a determines
that a notification has been made to the content management server 600a
that the content-using device 700a is online. Subsequently, the
content-using device 700a updates the content management list 722a at
time point T17 (Step S215). A content management list 722b, which
corresponds to the content management list 722a following the update, is
as illustrated in FIG. 60. In the content management list 722b, which
corresponds to the content management list 722a following the update,
"1/22, 22:00" is set in a scheduled expiration time field 737b, and
"1/23, 22:00" is set in a scheduled expiration time field 741b.

[0590] Here, for instance, the validity duration of the content "Cont1" is
"24H", and hence, the scheduled expiration time for the content "Cont1"
is time point T19, which is calculated by adding "24H" to time point T16.
In other words, the content "Cont1" is available for use, following time
point T17, from time point T16 to time point T19.

[0591] In the description provided above, the content-using device 700a
returns to online once again at 22:00, January 21st. However, when
the content-using device 700a does not return to online once again by
23:00, January 21st, which corresponds to the scheduled expiration
time of the content "Cont1", the content-using device 700a is unable to
use the content "Cont1" following 23:00, January 21st even when
transmitting a polling command to the content management server 600a at a
given point following 23:00, January 21st. This is since the
scheduled expiration time of the content "Cont1" has already passed.

[0592] 4.7. Effects Achieved by Embodiment 4

[0593] In embodiment 4, the content-using device performs polling with
respect to the content management server at regular intervals. When
receiving a polling command transmitted from the content-using device,
the content management server determines that the content-using device
having transmitted the polling command is online. When the content-using
device requests for continuous use of a content even after a period of
validity of the content has expired, the content-using device needs to
perform polling with respect to the content management server, which is
realized by the present embodiment. On the other hand, the content
management server need not perform polling with respect to the
content-using device in such a case. In addition, a content-using device
that does not request for continuous use of a content whose scheduled
expiration time has already passed does not perform polling. As such,
traffic on the communication path can be reduced according to the present
embodiment.

[0594] Further, according to the present embodiment, even when the
content-using device transitions from online to offline during use of a
content, the content-using device can extend the scheduled expiration
time set to the content by performing polling with respect to the content
management server within the period of validity of the content. As such,
the content-using device need not be kept in an online state at all
times.

5. Other Modifications

[0595] In the above, description has been provided on the present
invention with reference to exemplary embodiments thereof. However, and
as a matter of course, the present invention should not be construed as
being limited to the embodiments above. For instance, at least the
modifications such as presented in the following are included within the
spirit and scope of the present invention.

[0596] (1) In embodiments 2, 3, and 4, the content management server, once
determining that the content-using device is offline, no longer performs
the online/offline detection, which involves performing polling at hourly
intervals, with respect to the content-using device. However, the present
invention is not limited to this.

[0597] That is, so as to simplify control to be performed by the content
management server, the content management server may be configured to
perform processing as described in the following.

[0598] The content management server performs polling at uniform intervals
with respect to all content-using devices registered to the content-using
device list, regardless of whether or not each of the content-using
devices is online.

[0599] In addition, so as to reduce network traffic, the frequency at
which the content management server performs polling with respect to
content-using devices may be decreased to some degree.

[0600] (2) In embodiments 2, 3, and 4, the content management server/the
content-using device may append signature data to polling commands,
polling Ack signals, and online control signals transmitted therebetween.
The provision of signature data to such signals serves as a
countermeasure for preventing unauthorized copying of the signals. Note
that, as already described above, an online control signal is a
notification signal transmitted by the content-using device to the
content management server when the content-using device self-detects an
online state thereof.

[0601] In specific, the content management server/the content-using device
generates signature data for each of the polling command, the polling Ack
signal, and the online control signal by performing digital signature.
Here, the generation of signature data is performed by using, for
instance, a private key that is stored only to authentic devices.
Subsequently, the signature data so generated are appended to each of the
polling command, the polling Ack signal, and the online control signal.
Subsequently, the polling command, the polling Ack signal, and the online
control signal having signature data appended thereto are transmitted to
the content management server/the content-using device.

[0602] The content management server/the content-using device receives the
polling command, the polling Ack signal, and the online control signal
having signature data appended thereto. Subsequently, verification of the
signature data provided to the polling command, the polling Ack signal,
and the online control signal so received is performed by using a public
key corresponding to the private key. Only when the verification is
successful, the content management server/the content-using devices use
the polling command, the polling Ack signal, and the online control
signal so received.

[0603] Here, the RSA signature method may be used as one example of a
method for providing a digital signature to a command or a signal.

[0604] (3) In embodiment 3, each of a signal indicating the invalidation
instruction and a signal indicating the invalidation response may have
signature data identifying the content management server/the
content-using device appended thereto for the purpose of preventing
unauthorized copying thereof.

[0605] The generation of the signature data to be appended to such signals
is performed in the above-described manner, by using a private key that
is stored only to authentic devices and by performing digital signature
with respect to the signals. Here, the RSA signature method may be used
as one example of a method for providing a digital signature to a command
or a signal.

[0606] On the side of the content-using device, verification is performed
of whether signature data appended to such signals corresponds to an
authentic content management server, and invalidation of an
invalidation-target content is performed when the verification is
successful. Note that the content-using device performs invalidation of
an invalidation-target content by deleting the content, controlling
operations of an application (i.e., by prohibiting playback upon
recognition of playback of the content or the like), or deleting a key
corresponding to the content.

[0607] FIG. 61 illustrates one example of a data configuration of an
invalidation instruction. As illustrated in FIG. 61, an invalidation
instruction 351 includes an invalidation command 352, a content
management server name 353, a content-using device name 354, a content ID
355, and signature data 356.

[0608] The content management server generates a concatenated data by
concatenating the invalidation command 352, the content management server
name 353, the content-using device name 354, and the content ID 355.
Subsequently, the content management server generates the signature data
356 by performing digital signature (S) with respect to the concatenated
data so generated. Here, when performing the digital signature (S), the
content management server uses a private key 361 held therein.
Subsequently, the content management server generates the invalidation
instruction 351 by appending the signature data 356 to the concatenated
data.

[0610] The content-using device, when receiving the invalidation
instruction 351, checks whether or not a content-using device name
corresponding thereto is included in the invalidation instruction 351 so
received. When a content-using device name that corresponds to the
content-using device is not included in the invalidation instruction 351,
the content-using device determines that the invalidation instruction is
addressed thereto and discards the invalidation instruction 351 received.

[0611] When a content-using device name that corresponds to the
content-using device is included in the invalidation instruction 351, the
content-using device verifies the authenticity of the signature data 356
included in the invalidation instruction 351 by using a public key
corresponding to the private key 361. When the authenticity of the
signature data 356 cannot be determined, the content-using device
discards the invalidation instruction 351 received. Further, the
content-using device may be further configured so as to transmit, to the
content management server, a notification indicating that the
authenticity of the signature data 356 could not be determined in such a
case.

[0612] When the authenticity of the signature data 356 is determined, the
content-using device invalidates a content that has been provided from
the content management server and that corresponds to the content ID 355
according to the invalidation command 352 included in the invalidation
instruction 351 received.

[0613] An invalidation response may have the same data configuration as
the invalidation instruction described above.

[0614] (4) In embodiments 2, 3, and 4, the content management sever
manages the content-using device list and the offline device list as
separate lists. However, the present invention is not limited to the
management of lists being performed in such a manner.

[0615] That is, the content-using device list and the offline device list
may be combined into a single content-using device list. In such a case,
in the combined content-using device list, offline content-using devices
may be indicated by providing, only to device information pieces
corresponding to offline content-using devices, indication in the form of
ticks or checks. In addition to this, the management of offline
content-using devices may also be performed by providing, to each device
information piece corresponding to an offline content-using device, an
indication of a time point at which the corresponding content-using
device has been detected as being offline.

[0616] (5) In embodiments 2, 3, and 4, polling is performed by the content
management server at hourly intervals. However, the present invention is
not limited to this.

[0617] That is, the polling may be performed once every two hours, once
every six hours, once every twelve hours, etc., provided that the polling
is performed at regular intervals. Further, polling may be performed with
longer intervals therebetween during the nighttime compared to during the
day time. Further, the frequency at which polling is performed may be
determined depending upon load exerted upon applications and
communication traffic.

[0618] Alternatively, the frequency at which polling is performed may be
determined depending upon relative validity durations of contents. For
instance, when a relative validity duration of a given content is ten
hours, the polling may be performed once every two hours. By polling
being performed in such a manner, even when a content-using device
transitions from online to offline immediately before an invalidation
instruction is transmitted thereto for invalidating a given content, the
content is invalidated in twelve-hours' time, if not sooner, by the
period of validity of the content expiring.

[0619] Alternatively, when a relative validity duration of a given content
is ten days, polling may be performed once every two days. By polling
being performed in such a manner, even when a content-using device
transitions from online to offline immediately before an invalidation
instruction is transmitted thereto for invalidating a given content, the
content is invalidated in twelve days, if not sooner, by the period of
validity of the content expiring.

[0620] In addition, it can be assumed that a relative validity duration of
a given content is set in relation to the value of the given content. Due
to this, a content having high value may be provided with a short
relative validity duration. Further, in such a case, polling intervals
may be determined in accordance with the relative validity duration of
the content. By setting the relative validity duration for a content
having high value so as to be shorter than a relative validity duration
for a content of less value, the management of the timing at which
invalidation of the content is performed when invalidation of the content
is desired can be performed with an increase degree of accuracy.

[0621] (6) In embodiments 2, 3, and 4, the same relative validity duration
is set with respect to one content regardless of the different
content-using devices to which the content is provided. However, the
present invention is not limited to this.

[0622] That is, different relative validity durations may be set with
respect to a single content so as to correspond to the different
content-using devices to which the content is provided. For instance,
when a single content is shared by different users, when the reliability
of a specific one of the users is high, the relative validity duration
corresponding to the specific user may be set so as to be longer than
those for other users.

[0623] (7) In embodiments 2, 3, and 4, when the content-using device
transitions from offline to online, the content-using device notifies the
content management server of the transition from offline to online.
However, the present invention is not limited to this, and the
content-using device need not make such a notification provided that the
content management server performs polling continuously.

[0624] (8) In embodiment 3, description has been provided that displaying
is performed of the state of invalidation. However, the present invention
is not limited to this, and such displaying need not be performed. That
is, accumulation may be performed of invalidation states, and reference
may be made to such invalidation states only when necessary.

[0625] (9) In embodiments 2, 3, and 4, when the content-using device
self-detects an online state, the content-using device makes a
notification indicating an online state thereof to the content management
server in the form of the online control signal. However, there may be
cases where, even when a content-using device transmits an online control
signal, the content management server cannot receive the online control
signal for reasons such as the content management server being
powered-off.

[0626] In such cases, the content-using device may repeatedly transmit the
online control signal to the content management server until a response
is received from the content management server indicating that the online
control signal has been received.

[0627] Alternatively, a supplementary server may be separately provided.
When a supplementary server is provided, the content-using device
transmits the online control signal to the supplementary server. The
supplementary server, when receiving the online control signal, stores
the online control signal. Subsequently, the supplementary server reads
out the online control signal stored therein. Following the reading of
the online control signal, the supplementary server repeatedly transmits
the online control signal to the content management server until a
response is received from the content management server indicating that
the online control signal has been received.

[0628] In the above-described case where a supplementary server is
provided, the content management server, upon recovery, may first refer
to the supplementary server and thereby obtain the online control signal
from the supplementary server. Subsequently, the content management
server performs processing such as the deletion, from the offline device
list, of the content-using device having issued the online control signal
and the updating of the content management list by using the online
control signal obtained from the supplementary server. Further, when
having output, to a content-using device, an invalidation instruction for
invalidating the playback of a content by the content-using device, the
content management server may, upon recovery, refer to the supplementary
server. Subsequently, the content management server tries to acquire an
online control signal. When an online control signal is successfully
acquired from the supplementary server, the content management server
transmits the invalidation instruction once again to the content-using
device, which has now become online.

[0629] Alternatively, the content distribution system may be configured as
described in the following.

[0630] As illustrated in FIG. 62, a content distribution system 50
pertaining to one aspect of the present invention includes: a content
management sever 800a; a content-using device 900a; and a relay server
950a. In the content distribution system 50, the content management
server 800a and the relay server 950a are connected via a network.
Further, the content-using device 900a and the relay server 950a are also
connected via a network.

[0631] The following explains purposes as to why the relay server 950a is
incorporated in the content distribution system 50.

[0632] The relay server 950a substitutes for the content management server
800a. The content management server 800a, after making a request for
substitution to the relay server 950a, may be powered-off. Subsequently,
when the content management server 800a is later powered-on, the relay
server 950a transmits information accumulated therein to the content
management server 800a.

[0633] (9-1) Operations of Content Distribution System 50 (Part 1)

[0634] In the following, description is provided on operations (part 1) of
the content distribution system 50, with reference to the sequence
diagram illustrated in FIG. 63.

[0635] The content management server 800a transmits, to the relay server
950a, an instruction for polling, an address, and a timing for performing
polling (Step S601).

[0636] The content management server 800a transitions to a power-off state
(Step S612).

[0637] The relay server 950a receives, from the content management server
800a, the instruction for polling, the address, and the timing for
performing polling (Step S601). Subsequently, the relay server 950a
stores therein the instruction for polling, the address, and the timing
for performing polling received from the content management sever 800a
(Step S602). Then, the relay server 950a makes a comparison between the
current time point and the timing stored therein, and determines whether
the current time point matches the timing stored therein (Step S603).
When the current time point does not match the timing stored therein
("NO" in Step S603), the relay server 950a returns to the processing in
Step S603 and performs processing once again from Step S603.

[0638] When the current time point matches the timing stored therein
("YES" in Step S603), the relay server 950a generates a polling command
by using the polling instruction and the address stored therein (Step
S604). Subsequently, the relay server 950a transmits the polling command
so generated to the content-using device 900a (Step S605).

[0641] At this point, the content management server 800a transitions to a
power-on state (Step S613).

[0642] Subsequently, the relay server 950a checks whether a connection is
established with the content management server 800a (Step S609). When
determining that the content management server 800a is not connected
therewith ("NO" in Step S610), the relay server 950a returns to Step S609
and performs processing from Step S609 once again. When determining that
the content management server 800a is connected therewith ("YES" in Step
S610), the relay server 950a reads out the polling Ack stored therein.
Subsequently, the relay server 950a transmits the polling Ack so read out
to the content management server 800a (Step S611).

[0643] (9-2) Operations of Content Distribution System 50 (Part 2)

[0644] In the following, description is provided on operations (part 2) of
the content distribution system 50, with reference to the sequence
diagram illustrated in FIG. 64.

[0645] The content-using device 900a transmits, to the relay server 950a,
an instruction for polling, an address, and a timing for performing
polling (Step S621).

[0646] The relay server 950a receives, from the content-using device 900a,
the instruction for polling, the address, and the timing for performing
polling (Step S621). Subsequently, the relay server 950a stores therein
the instruction for polling, the address, and the timing for performing
polling received from the content-using device 900a (Step S622).
Subsequently, the relay server 950a makes a comparison between the
current time point and the timing stored therein, and determines whether
the current time point matches the timing stored therein (Step S623).
When the current time point does not match the timing stored therein
("NO" in Step S623), the relay server 950a returns to Step S623 and
performs processing from Step S623 once again.

[0647] When the current time point matches the timing stored therein
("YES" in Step S623), the relay server 950a generates a polling command
by using the polling instruction and the address stored therein (Step
S624). Subsequently, the relay server 950a transmits the polling command
generated to the content management server 800a (Step S625).

[0653] The content management server 800a transitions to a power-off state
(Step S654).

[0654] The relay server 950a receives the invalidation instruction from
the content management server 800a (Step S642). Subsequently, the relay
server 950a stores therein the invalidation instruction received from the
content management server 800a (Step S643). Then, the relay server 950a
makes a comparison between the current time point and a timing stored
therein. Here, the timing stored in the relay server 950a indicates a
time point at which the invalidation instruction is to be transmitted to
the content-using device 900a. The relay server 950a determines whether
the current time point matches the timing stored therein (Step S644).
When the current time point does not match the timing stored therein
("NO" in Step S644), the relay server 950a returns to Step S644 and
performs processing from Step S644 once again.

[0655] When the current time point matches the timing stored therein
("YES" in Step S644), the relay server 950a checks whether a connection
is established with the content-using device 900a (Step S645). When
determining that the content-using device 900a is not connected therewith
("NO" in Step S646), the relay server 950a returns to Step S644 and
performs processing from Step S644 once again. When determining that the
content-using device 900a is connected therewith ("YES" in Step S646),
the relay server 950a reads out the invalidation instruction stored
therein. Subsequently, the relay server 950a transmits the invalidation
instruction read out to the content-using device 900a (Step S647).

[0658] At this point, the content management server 800a transitions to a
power-on state (Step S655).

[0659] Subsequently, the relay server 950a checks whether a connection is
established with the content management server 800a (Step S651). When
determining that the content management server 800a is not connected
therewith ("NO" in Step S652), the relay server 950a returns to Step S651
and performs processing from Step S651 once again. When determining that
the content management server 800a is connected therewith ("YES" in Step
S652), the relay server 950a reads out the invalidation response stored
therein. Subsequently, the relay server 950a transmits the invalidation
response read out to the content management server 800a (Step S653).

[0660] (9-4) Operations of Content Distribution System 50 (Part 4)

[0661] In the following, description is provided on operations (part 4) of
the content distribution system 50 which differ from the operations
described above, with reference to the sequence diagram illustrated in
FIG. 66.

[0662] The content management server 800a generates an invalidation
instruction for invalidating a given content with respect to the
content-using device 900a (Step S661). The invalidation instruction
includes a content-using device name identifying the content-using device
900a. Subsequently, the content management server 800a transmits the
invalidation instruction so generated to the relay server 950a (Step
S662).

[0665] The relay server 950a receives the polling command from the
content-using device 900a (Step S664). Subsequently, the relay server
950a extracts the content-using device name from the polling command
received. Then, the relay server 950a searches, among invalidation
instructions stored therein, for an invalidation instruction including
the same content-using device name as the content-using device name
extracted (Step S665). When an invalidation instruction including the
same content-using device name exists ("Exists" in Step S666), the relay
server 950a generates a response that includes the invalidation
instruction including the same content-using device name and that
includes indication that an invalidation instruction including the same
content-using device name exists (Step S667). On the other hand, when an
invalidation instruction including the same content-using device name
does not exist ("Does not exist" in Step S666), the relay server 950a
generates a response that includes indication that an invalidation
instruction including the same content-using device name does not exist
(Step S668). Subsequently, the relay server 950a transmits the response
generated to the content-using device 900a (Step S669).

[0666] The content-using device 900a receives a response from the relay
server 950a (Step S669). Subsequently, the content-using device 900a
determines whether or not an invalidation instruction exists according to
the response received (Step S670). When an invalidation instruction does
not exist ("Invalidation instruction does not exist" in Step S670), the
content-using device 900a does not perform any processing. When an
invalidation instruction exists ("Invalidation instruction exists" in
Step S670), the content-using device 900a performs invalidation
processing according to the invalidation instruction included in the
response (Step S671). Subsequently, the content-using device 900a
generates an invalidation response indicating that the invalidation
processing has been completed, and transmits the invalidation response
generated to the relay server 950a (Step S672).

[0668] (10) In embodiment 4, the content-using device may transmit polling
commands at regular intervals. In addition, the time point at which
polling is to be performed may set in view of a schedule expiration time.
For instance, the content-using device may transmit a polling command at
a time point that precedes the scheduled expiration time by a
predetermined period of time.

[0669] By configuring the content-using device so as to perform the
transmission of the polling command at regular intervals, the content
management server is able to perform the determination of whether or not
the content-using device is online or offline at regular intervals.

[0670] In addition, by configuring the content-using device so as to
transmit the polling command at time points set taking into consideration
a scheduled expiration time, traffic load can be decreased.

[0671] (11) In embodiment 3, the content management server transmits an
invalidation instruction to the content-using device. However, the
present invention is not limited to this.

[0672] That is, the content management server may transmit an instruction
for changing conditions of use of a content to the content-using device
instead of transmitting an invalidation instruction. The content-using
device, when receiving the instruction for changing conditions of use of
a content from the content management server, changes the conditions of
use applied to the content immediately.

[0673] Note that here, the conditions of use of a given content may
include conditions pertaining to playback of the content, conditions
pertaining to the copying and the redistribution of the content,
conditions pertaining to secondary use of the content, etc. In specific,
the conditions pertaining to playback of the content are, for instance,
the number of times the content can be played back, the resolution
applied to the content when played back, and the length of the validity
duration of the content. Further, conditions pertaining to the copying
and the redistribution of the content are, for instance, the number of
times the content can be copied, and a range of users to which the
content can be redistributed. Finally, the conditions pertaining to
secondary use of the content are, for instance, whether or not partial
use of the content is permitted, etc.

[0674] The content-using device, when receiving the instruction for
changing conditions of use of the content from the content management
server, is able to immediately change the conditions of use applied to
the content.

[0675] Further, when the content-using device is offline when the content
management server has transmitted the instruction for changing conditions
of use of the content thereto, processing is performed as described in
the following.

[0676] When the content-using device, which was previously offline,
transitions from offline to online, makes an inquiry to the content
management server. In response to the inquiry made from the content-using
device, the content management server transmits new conditions of use of
the content along with the content or a key. The content-using device,
when receiving the new conditions of use of the content, updates the
conditions of use of the content with the new conditions of use of the
content so received.

[0677] In addition, in embodiment 3, the content-using device stops the
use of a content or invalidates the content when the validity duration of
the content expires. However, the present invention is not limited to
this. That is, the content-using device may determine in advance and hold
default conditions of use of the content, and when the validity duration
of the content expires, may refer to the default conditions of use of the
content.

[0678] (12) The content-using device may delete a content stored thereby
as described in the following. Note that the deletion of the content by
the content-using device as described in the following is referred to
hereinafter as "self-deletion" of the content.

[0679] In embodiment 2, when a user performs user operations with respect
to the content-using device 200 before the scheduled expiration time of
the content is reached, the content-using device 200 may perform
self-deletion of the content.

[0680] (12-1) The following describes operations involved in self-deletion
performed by the content-using device 200 when deleting a content
identified by "Cont1" in the content ID field 251 included in the content
management list 222 in FIG. 12 before "1/20, 23:30" indicated in the
scheduled expiration time field 254. Note that, the content-using device
200 is currently offline when performing the self-deletion in this
example.

[0681] First, the content management control unit 221 deletes the content
"Cont1". Subsequently, the content management control unit 221
additionally writes, to the scheduled expiration time field 254
corresponding to the content ID "Cont1" in the content ID field 251 in
the content management list 222, information indicating that "the content
has already been deleted".

[0682] Here, the content management control unit 221 may additionally
write, to the scheduled expiration time field 254, a time point at which
the content "Cont1" has been self-deleted by the content-using device
200. In addition, the determination of whether or not to additionally
write, to the scheduled expiration time field 254, the time point at
which the content has been self-deleted may be made depending upon
specifications made with respect to the content-using device 200. In
addition, whether or not the time point at which the content "Cont1" has
been self-detected is to be written to the scheduled expiration time
field 254 in the content management list 222 may be specified by the
content management server 100 as one of the rules pertaining to the use
of the content "Cont1".

[0683] Subsequently, the content-using device 200, when transitioning from
offline to online once again, outputs the online control signal
indicating the transition from offline to online to the content
management server 100. Here, along with the online control signal, the
content-using device 200 may notify the content management server 100 of
the actual time point at which the content "Cont1" has been self-deleted.
When receiving such a notification from the content-using device 200, the
content management control unit 130 of the content management server 100
updates the content management list 131 so as to be consistent with the
information included in the notification.

[0684] Subsequently, the content management control unit 221 of the
content-using device 200 deletes the content "Cont1" from the content
management list 222.

[0685] In the following, description is provided on operations of the
content-using device 200 when performing self-deletion of a content
before the scheduled expiration time set with respect to the content is
reached, with reference to the sequence diagram illustrated in FIG. 67.

[0686] The content management control unit 221 of the content-using device
200 receives a content ID identifying a content that is to be
self-deleted (Step S701).

[0688] Subsequently, the content management control unit 221 determines
whether the current time point is before the scheduled expiration time
included in the content management information piece read out (Step
S703).

[0689] When determining that the current time point is before the
scheduled expiration time ("YES" in Step S703), the content management
control unit 221 receives a specification of whether or not to store a
time point at which the self-deletion is performed (Step S704).
Subsequently, the content management control unit 221 deletes the content
identified by the content ID from the content storage unit 224 (Step
S705).

[0690] Following the deletion of the content, when a specification has
been made for storing the time point at which the self-deletion is
performed ("Made" in Step S706), the content management control unit 221
writes, to the scheduled expiration time included in the content
management information piece, an indication of "Deleted" and the time
point at which the self-deletion has been performed. On the other hand,
when a specification has not been made for storing the time point at
which the self-deletion is performed ("Not made" in Step S706), the
content management control unit 221 writes, to the scheduled time
included in the content management information, an indication of
"Deleted".

[0692] When the content-using device 200 is connected with the content
management server 100 ("YES" in Step S709), the online control
transmission unit 213 notifies the content management server 100 that the
content has been deleted (Step S710).

[0694] The online control reception unit 113 of the content management
server 100 receives a notification indicating that the content has been
deleted from the content-using device 200 (Step S710). Subsequently, the
content management control unit 130 deletes, from the content management
list 131, a usage device information piece included in the corresponding
management information piece. Here, the corresponding management
information piece includes a content ID identifying the content having
been deleted. In addition, the usage device information piece includes a
usage device name identifying the content-using device having deleted the
content (Step S712).

[0695] (12-2) The following describes operations involved in self-deletion
performed by the content-using device 200 when deleting a content
identified by "Cont2" in the content ID field 255 included in the content
management list 222a illustrated in FIG. 12 while the content-using
device 200 is online.

[0696] Note that in the content management list 222a, "---" is stored in
the scheduled expiration time field corresponding to the content while
the content-using device 200 is online. The indication of "---" as the
scheduled expiration time indicates that the viewing of the content can
be performed whenever desired and for an unlimited period of time as long
as the content-using device 200 is online.

[0697] The content-using device 200 deletes the content. Subsequently, the
content-using device 200 notifies the content management server 100 that
the content has been deleted.

[0698] The content management server 100 immediately updates the content
management list 131 so as to be consistent with the deletion of the
content.

[0700] Here, note that the content management server 100 may be configured
to keep a record of the deletion of the content. That is, the content
management server 100 may keep a record indicating that the content was
once shared with the content-using device but later deleted by the
content-using device. By configuring the content management server 100 in
such a manner, the content management server 100, when issuing an
invalidation instruction, may display the following message, for example,
by referring to the record.

[0701] "Cont1 was used by C1, C2, and C3. Cont1 provided to each of C1,
C2, and C3 has been invalidated immediately. Cont1 provided to C1 was
deleted before the instruction for invalidation was made."

[0702] As a matter of course, the above message may be replaced by the
following message: "Cont1 was used by C1, C2, and C3. Cont1 provided to
each of C1, C2, and C3 has been invalidated immediately."

[0703] In the following, description is provided on operations of the
content-using device 200 when performing self-detection of a content
before the scheduled expiration time set with respect to the content is
reached, with reference to the sequence diagram illustrated in FIG. 68.

[0704] The content management control unit 221 of the content-using device
200 receives a content ID identifying a content to be self-deleted (Step
S721).

[0709] The online control reception unit 113 of the content management
server 100 receives a notification indicating that the content has been
deleted from the content-using device 200 (Step S724). Subsequently, the
content management control unit 130 deletes, from the content management
list 131, a usage device information piece included in the corresponding
management information piece. Here, the corresponding management
information piece includes a content ID identifying the content having
been deleted. In addition, the usage device information piece includes a
usage device name identifying the content-using device having deleted the
content (Step S726).

[0710] (13) Modification may be performed as described in the following.

[0711] For instance, the content-using device 200 includes: the
online/offline notification detection unit 201; the content control unit
202; and the time measurement unit 203, as illustrated in FIG. 2. Each of
the online/offline notification detection unit 201, the content control
unit 202, and the time measurement unit 203 is implemented as a
combination of a CPU and an application program stored onto a memory.

[0712] As such, in the content-using device 200, a plurality of
application programs (hereinafter referred to simply as "applications")
are caused to operate. By such applications operating, the online/offline
notification detection unit 201, the content control unit 202, and the
time measurement unit 203 are each able to realize the respective
functions.

[0713] When multiple applications are operated in the content-using device
200, each application is either in (a) a state where the application is
launched and operating or (b) a state where the application is launched
and operating in the background.

[0714] In specific, the content control unit 202, which is one of the
applications, measures the elapse of a period of validity of a content
having a scheduled expiration time set thereto.

[0715] At one point in processing, the content control unit 202 may be in
either one of the two states (a) and (b) described above.

[0716] The content control unit 202, in either one of the two states (a)
and (b), measures the elapse of a period of validity of a content having
a period of validity set thereto.

[0717] The content control unit 202 includes a counter unit and other
processing units. The counter unit measures the elapse of the period of
validity of the content having a period of validity set thereto. When the
content control unit 202 is in state (b), the counter unit, alone, is in
state (a) at all times.

[0718] The content control unit 202 may be configured to measure the
elapse of the period of validity of the content having a period of
validity set thereto when in state (a). Alternatively, the content
control unit 202 may be configured not to measure the elapse of the
period of validity when in state (b).

[0720] The content management information piece 266 includes: "Cont1" in
the content ID field 251; "24H" in the relative validity duration field
252; "S1" in the content management server name field 253; and "1/20,
23:30" in the scheduled expiration time field 254. The content management
information piece 266 indicates that the content-using device 200 is not
connected with the content management server "S1" and that the
content-using device 200 is offline.

[0721] The content management information piece 267 includes: "Cont2" in
the content ID field 255; "48H" in the relative validity duration field
256; "S1" in the content management server name field 257; and "1/21,
23:30" in the scheduled expiration time field 258. The content management
information piece 267 also indicates that the content-using device 200 is
not connected with the content management server "S1" and that the
content-using device is offline.

[0722] The content management information piece 268b includes: "Cont3" in
the content ID field 259; "24H" in the relative validity duration field
260; "S2" in the content management server name field 261; and "---" in a
scheduled expiration time field 262b. The content management information
piece 268b indicates that the content "Cont3" has been supplied from the
content management server "S1". Further, the content management
information piece 268b also indicates that the content-using device 200
is connected with the content management server "S2" and that the
content-using device is online.

[0723] As such, the content-using device is not connected with a first
content management server, and thus, is offline with respect to the first
content management server. In contrast, the content-using device is
connected with a second content management server, and thus, is offline
with respect to the second content management server.

[0724] (15) The content management server distributes a personal content
to the content-using device. The content-using device uses the content.
Later, the content-using device, upon being provided with instructions
from the content management server, stops playback of the personal
content accumulated therein or invalidates the personal content
accumulated therein.

[0725] By deletion of a personal content being performed in such a
concern-free manner, a person who desires to distribute a content is able
to distribute the content without any concerns.

[0726] The content management server determines an online/offline state of
the content-using device by performing polling with respect to the
content-using device. When the content-using device is in online, the
content management server transmits an invalidation instruction
instructing the content-using device to invalidate playback of a content
via the communication path. On the other hand, when the content-using
device is offline, the content-using device performs self-detection of
the offline state thereof by detecting deactivation of an communication
module or the like, and performs control such that playback of a content
is automatically invalidated when a period of validity of the content
expires. The content management server, when the content-using device is
offline, is able to keep track of whether or not the content has been
invalidated by managing the period of validity of the content.

[0727] (16) Examples of the content as described above include: music
data, audio data, a moving image, a still image, movie data constituted
of a moving image and audio data, a database, a spreadsheet, text data,
and a computer program.

[0728] The use/playback of a content as discussed above may refer to
playing back music data, audio data, a moving image, a still image, or
movie data constituted of a moving image and audio data. In addition, the
use/playback of a content as discussed above may refer to performing
operations such as reading out, writing into, updating, and displaying
with respect to data stored in a database or a spreadsheet, or text data.
Further, the use/playback of a content as discussed above may refer to
causing a processor to operate in accordance with a computer program.

[0729] (17) The present invention may be implemented as described in the
following.

[0730] Another aspect of the present invention is a content-using device
that holds and uses a content distributed thereto from a content
management server, comprising: a detection unit that detects whether the
content-using device is in an online state of being connected with the
content management server or in an offline state of being unconnected
with the content management server; a setting unit that sets a period of
validity for using the content when the content-using device is detected
as being in the offline state; and a control unit that monitors elapse of
the period of validity, and permits the use of the content before the
elapse of the period of validity and prohibits the use of the content
after the elapse of the period of validity.

[0731] In the content-using device, the detection unit may output a
detection time at which the offline state of the content-using device is
detected, and the control unit may hold a relative validity duration
during which the use of the content is permitted and may calculate the
period of validity by adding the relative validity duration to the
detection time when the content-using device is detected as being in the
offline state.

[0732] In the content-using device, when the detection unit detects that
the content-using device is in the online state at a time point after the
period of validity is set with respect to the content due to the
content-using device being previously detected as being in the offline
state and before the elapse of the period of validity, the setting unit
may cancel the period of validity set with respect to the content, and
when the period of validity is not set with respect to the content, the
control unit may permit the use of the content at all times.

[0733] In the content-using device, the setting unit may hold a content
management list in which a content identifier identifying the content and
the relative validity duration are stored in an associated state, and may
store the period of validity of the content in association with the
content identifier in the content management list when the content-using
device is detected as being in the offline state, and the control unit
may monitor the elapse of the period of validity stored in the content
management list.

[0734] In the content-using device, when the detection unit detects that
the content-using device is in the online state at a time point after the
period of validity is set with respect to the content due to the
content-using device being previously detected as being in the offline
state and before the elapse of the period of validity, the setting unit
may delete the period of validity stored in the content management list.

[0735] The content-using device may further comprise a reception unit that
receives, from the content management server, an invalidation instruction
for invalidating the content, wherein the setting unit may set a second
period of validity for using the content when the invalidation
instruction is received, and the control unit may monitor elapse of the
second period of validity of the content and may permit the use of the
content before the elapse of the second period of validity and prohibit
the use of the content after the elapse of the second period of validity.

[0736] The content-using device may further comprise a
transmission/reception unit that performs polling with respect to the
content management server and receives a first response to the polling
from the content management server, wherein the setting unit may set a
third period of validity for use of the content when the first response
is received, and the control unit may monitor elapse of the third period
of validity of the content and may permit the use of the content before
the elapse of the third period of validity and prohibit the use of the
content after the elapse of the third period of validity.

[0737] In the content-using device, the transmission/reception unit may
perform polling with respect to the content management server before the
elapse of the third period of validity and may receive a second response
to the polling from the content management server, the setting unit may
set a fourth period of validity for use of the content when the second
response is received, and the control unit may monitor elapse of the
fourth period of validity of the content and may permit the use of the
content before the elapse of the fourth period of validity and prohibit
the use of the content after the elapse of the fourth period of validity.

[0738] Another aspect of the present invention is a content-using device
that holds and uses a content distributed thereto from a content
management server, comprising: a detection circuit that detects whether
the content-using device is in an online state of being connected with
the content management server or in an offline state of being unconnected
with the content management server; a setting circuit that sets a period
of validity for using the content when the content-using device is
detected as being in the offline state; and a control circuit that
monitors elapse of the period of validity, and permits the use of the
content before the elapse of the period of validity and prohibits the use
of the content after the elapse of the period of validity.

[0739] Another aspect of the present invention is an integrated circuit
incorporated in a content-using device that holds and uses a content
distributed thereto from a content management server, comprising: a
detection circuit that detects whether the content-using device is in an
online state of being connected with the content management server or in
an offline state of being unconnected with the content management server;
a setting circuit that sets a period of validity for using the content
when the content-using device is detected as being in the offline state;
and a control circuit that monitors elapse of the period of validity, and
permits the use of the content before the elapse of the period of
validity and prohibits the use of the content after the elapse of the
period of validity.

[0740] Another aspect of the present invention is a content-using device
that holds and uses a content distributed thereto from a content
management server, comprising: a memory unit that stores a computer
program being a combination of a plurality of computer instructions; and
a processor that fetches, from the computer program stored in the memory
unit, the computer instructions one by one, reads the computer
instructions fetched, and operates according to a result of the reading,
wherein the computer program causes a computer to: detect whether the
content-using device is in an online state of being connected with the
content management server or in an offline state of being unconnected
with the content management server; set a period of validity for using
the content when the content-using device is detected as being in the
offline state; and perform control of monitoring elapse of the period of
validity, and permitting the use of the content before the elapse of the
period of validity and prohibiting the use of the content after the
elapse of the period of validity.

[0741] Another aspect of the present invention is a computer program used
in a content-using device that holds and uses a content distributed
thereto from a content management server, comprising: a detection step of
detecting whether the content-using device, which is a computer, is in an
online state of being connected with the content management server or in
an offline state of being unconnected with the content management server;
a setting step of setting a period of validity for using the content when
the content-using device is detected as being in the offline state; and a
controlling step of monitoring elapse of the period of validity, and
permitting the use of the content before the elapse of the period of
validity and prohibiting the use of the content after the elapse of the
period of validity.

[0742] Another aspect of the present invention is a computer-readable
recording medium that stores thereon a computer program used in a
content-using device that holds and uses a content distributed thereto
from a content management server, wherein the computer program comprises:
a detection step of detecting whether the content-using device, which is
a computer, is in an online state of being connected with the content
management server or in an offline state of being unconnected with the
content management server; a setting step of setting a period of validity
for using the content when the content-using device is detected as being
in the offline state; and a controlling step of monitoring elapse of the
period of validity, and permitting the use of the content before the
elapse of the period of validity and prohibiting the use of the content
after the elapse of the period of validity.

[0743] Another aspect of the present invention is a content distribution
system including: a content management server that manages a content; and
a content-using device that uses the content, wherein the content
management server comprises: a first online/offline detection unit that
detects whether the content-using device is online or offline with
respect to the content management server; a device management unit that
manages an online/offline state of the content-using device; and a
content management unit that manages a state of use of the content in the
content-using device, and the content-using device comprises: a second
online/offline detection unit that detects whether the content-using
device is online or offline with respect to the content management
server; and a content control unit that manages a period of validity of
the content and controls the use of the content according to the
detection by the second online/offline control unit. This enables the
content-using device to perform the use of the content according to the
whether the content-using device is online or offline with respect to the
content management server. At the same time, the content management
server manages a state of use of the content in the content-using device.

[0744] According to the above-described aspect of the present invention,
management of the content according to the period of validity of the
content is possible after the content-using device becomes offline. In
addition, the content management server is able to perform management of
the content-using device which involves detecting whether the
content-using device is online or offline and determining when the period
of validity of the content expires. Further, by reflecting the results
obtained through such management to the management of the content, the
content management server is able to immediately acknowledge a state of
invalidation of the content when an invalidation instruction for
instructing the content-using device to invalidate the content is issued
with respect to the content-using device. This means that, in a case
where a given content has been distributed to several content-using
devices, the content management server is able to immediately acknowledge
how many of the content-using devices are online and have performed the
invalidation of the content. In addition, with regards to the content
devices that are offline, the content management server is able to
quickly acknowledge when the period of validity of the content expires in
each of the content-using devices. This enables a user is able to confirm
the invalidation of the content in each of the content-using devices that
the content has been distributed to, and therefore, is released from
concerns.

[0745] In the content distribution system, the content control unit of the
content-using device may commence management of the content according to
the period of validity of the content when the second online/offline
detection unit detects that the content-using device has transitioned
from online to offline, and may stop or deny the use of the content when
the period of validity of the content expires, and when the first
online/offline detection unit detects that the content-using device has
transitioned from online to offline, the device management unit may
register the content-using device as being offline, and the content
management unit may set a period of validity with respect to the content.
This enables the content-using device to perform the management of the
content according to the period of validity of the content only after
becoming offline with respect to the content management server.

[0746] In the content distribution system, the content control unit of the
content-using device may cancel the period of validity set with respect
to the content when the second online/offline detection unit detects that
the content-using device has transitioned from offline to online, and
when the first online/offline detection unit detects that the
content-using device has transitioned from offline to online, the device
management unit may cancel the offline registration of the content-using
device, and the content management unit may cancel the period of validity
set with respect to the content. This enables the content-using device to
not perform the management of the content according to the period of
validity of the content after the content-using device has become online
with respect to the content management server.

[0747] In the content distribution system, the content control unit of the
content-using device may update the period of validity set with respect
to the content when the second online/offline detection unit detects that
the content-using device is online, and when the first online/offline
detection unit of the content management server detects that the
content-using device is online, the content management unit may update
the period of validity set with respect to the content. This enables the
content-using device to perform the use of the content according to the
period of validity of the content and update the period of validity after
the content-using device becomes online with respect to the content
management server.

[0748] In the content distribution system, the content management server
may further comprise: an invalidation instruction reception unit that
receives an invalidation instruction for invalidation of the content; an
invalidation instruction transmission unit that transmits the
invalidation instruction to the content-using device; and an invalidation
response reception unit that receives an invalidation response from the
content-using device as a response to the invalidation instruction, the
content-using device may further comprise: an invalidation instruction
reception unit that receives the invalidation instruction from the
content management server when the content-using device is online; an
invalidation unit that invalidates the content according to the
invalidation instruction; and an invalidation response transmission unit
that generates an invalidation response when the content has been
invalidated and transmits the invalidation response to the content
management server, the invalidation instruction transmission unit of the
content management server transmits the invalidation instruction to the
content-using device according to (i) the online/offline state of the
content-using device managed by the device management unit or (ii) the
state of use of the content in the content-using device managed by the
content management unit, the device management unit of the content
management server updates the online/offline state of the content-using
device when the invalidation response is received from the content-using
device, and the content management unit of the content management server
updates the state of use of the content in the content-using device when
the invalidation response is received from the content-using device. This
enables the content management server to immediately instruct the
content-using device, when online, to perform the invalidation of the
content. On the other hand, this enables the content-using device, when
offline, to automatically invalidate the content after the period of
validity of the content expires.

[0749] Another aspect of the present invention is a content management
server in a content distribution system including the content management
server, which manages a content, and a content-using device that uses the
content, the content management server comprising: a first online/offline
detection unit that detects whether the content-using device is online or
offline with respect to the content management server; a device
management unit that manages an online/offline state of the content-using
device; and a content management unit that manages a state of use of the
content in the content-using device. This enables the content management
server to manage how the content is managed in the content-using device.

[0750] In the content management sever, when the first online/offline
detection unit detects that the content-using device has transitioned
from online to offline, the device management unit may register the
content-using device as being offline, and the content management unit
may set a period of validity with respect to the content. This enables
the content management server to manage, according to the online/offline
state of the content-using device, how the content is being managed in
the content-using device.

[0751] In the content management sever, when the first online/offline
detection unit detects that the content-using device has transitioned
from offline to online, the device management unit may cancel the offline
registration of the content-using device, and the content management unit
may cancel the period of validity set with respect to the content. This
enables the content management server to not perform the management of
the content according to the period of validity of the content after the
content-using device has become online with respect to the content
management server.

[0752] In the content management server, when the first online/offline
detection unit detects that the content-using device is online, the
content management unit may update the period of validity set with
respect to the content. This enables the content management server to
permit the content-using device, when online, to update the period of
validity set with respect to the content.

[0753] In the content management sever, the first online/offline detection
unit may perform polling with respect to the content-using device at a
predetermined timing, detect that the content-using device is online when
receiving a polling response from the content-using device in response to
the polling, and detect that the content-using device is offline when the
polling response is not received from the content-using device within the
predetermined interval. This enables the content management server to
detect whether the content-using device is online or offline.

[0754] In the content management sever, the first online/offline detection
unit may determine the predetermined timing according to a period of
validity of the content. This enables the content management server to
accurately manage, by using the content management unit, actually when
the period of validity of the content expires in the content-using
device.

[0755] In the content management server, the first online/offline
detection unit, when receiving polling from the content-using device at a
predetermined timing, may detect that the content-using device is
connected with the content management server, and transmit a polling
response to the content-using device. This enables the content management
server to detect that the content-using device is online, and to permit
the content-using device to update the period of validity set with
respect to the content.

[0756] In the content management server, the first online/offline
detection unit may detect that the content-using device is online when
receiving a notification from the content-using device that the
content-using device is online. This enables the content management
server to immediately detect that the content-using device, which was
previously offline, has become online.

[0757] The content management server further may comprise: an invalidation
instruction reception unit that receives an invalidation instruction for
invalidation of the content; an invalidation instruction transmission
unit that transmits the invalidation instruction to the content-using
device; and an invalidation response reception unit that receives an
invalidation response from the content-using device as a response to the
invalidation instruction, wherein the invalidation instruction
transmission unit of the content management server may transmit the
invalidation instruction to the content-using device according to (i) the
online/offline state of the content-using device managed by the device
management unit or (ii) the state of use of the content in the
content-using device manages by the content management unit, the device
management unit of the content management server may update the
online/offline state of the content-using device when the invalidation
response is received from the content-using device, and the content
management unit of the content management server may update the state of
use of the content in the content-using device when the invalidation
response is received from the content-using device. This enables the
content management server to immediately instruct the content-using
device, when online, to perform the invalidation of the content.

[0758] The content management server may further comprise an invalidation
display unit that displays a status of the invalidation of the content by
referring to the invalidation response received from the content-using
device, wherein the invalidation display unit, (i) may display
invalidation completion information indicating that the invalidation of
the content has been completed by the content-using device, when
connected with the content management server, and, (ii) may display a
period of validity of the content set in the content-using device, when
unconnected with the content management server. This enables the content
management server to acknowledge the status of the invalidation of the
content by the content-using device performed in accordance with the
invalidation instruction or the period of validity of the content.

[0759] The content management server may further comprise a display unit
that displays how the management of the content is being performed. This
enables a user of the content management server to acknowledge the
online/offline state of the content-using device and the period of
validity of the content.

[0760] Another aspect of the present invention is a content-using device
in a content distribution system including a content management server
that manages a content, and the content-using device, which uses the
content, the content-using device comprising: a second online/offline
detection unit that detects whether the content-using device is online or
offline with respect to the content management server; and a content
control unit that manages a period of validity of the content and
controls the use of the content according to the detection by the second
online/offline control unit. This enables the content-using device, when
offline, to perform the management of the content according to the period
of validity of the content.

[0761] In the content-using device, the content control unit may commence
management of the content according to the period of validity of the
content when the second online/offline detection unit detects that the
content-using device has transitioned from online to offline, and may
stop or deny the use of the content when the period of validity of the
content expires. This enables the content-using device to commence the
management of the content according to the period of validity of the
content when actually detected as being offline, and hence, to take full
advantage of the predetermined period of validity of the content.

[0762] In the content-using device, when the second online/offline
detection unit detects that the content-using device has transitioned
from offline to online, the content control unit may cancel the period of
validity set with respect to the content. This enables the content-using
device not to perform the management of the content according to the
period of validity of the content after the content-using device has
become online with respect to the content management server.

[0763] In the content-using device, after the second online/offline
detection unit detects that the content-using device is online, the
content control unit may update the period of validity set with respect
to the content at a point when the content-using device is detected as
being online. This enables the content-using device to update the period
of validity set with respect to the content according to permission from
the content management server receivable when connected with the content
management server.

[0764] In the content-using device, the second online/offline detection
unit may receive polling from the content management server at a
predetermined timing, generate a polling response as a response to the
polling, and transmit the polling response to the content management
server, and the second online/offline detection unit may detect that the
content-using device is online or offline by using either one of or any
combination of: a polling detection unit that detects whether or not the
polling is received at the predetermined timing; an activation detection
unit that detects activation of a communication module provided to the
content-using device; a detection unit that detects whether or not the
content-using device is located within a distance, from an access point,
within which radio signals from the content-using device reach the access
point; and a communication on/off operation detection unit that detects
whether or not a user operation of turning on/off communication has been
received. This enables the content-using device to detect the
online/offline state thereof with respect to the content management
device and thereby perform content control in accordance with the
online/offline state thereof.

[0765] In the content-using device, the second online/offline detection
unit, when detecting that the content-using device is online, may perform
polling with respect to the content management server and receive a
polling response from the content management server as a response to the
polling, and the content control unit, when the polling response permits
update of a period of validity set with respect to the content, may
perform the update of the period of validity set with respect to the
content. This enables the content-using device to receive a polling
response from the content management server and to update the period of
validity for using the content.

[0766] In the content-using device, the second online/offline detection
unit may determine a timing at which the polling is performed according
to the period of validity set with respect to the content. This enables
the content-using device to notify the content management server of when
the period of validity of the content expires with high accuracy.

[0767] In the content-using device, the second online/offline detection
unit, when detecting that the content-using device is online, may
transmit a notification to the content management server that the
content-using device is online, and the second online/offline detection
unit may detect that the content-using device is online or offline by
using either one of or any combination of: a polling detection unit that
detects whether or not the polling is received at the predetermined
timing; an activation detection unit that detects activation of a
communication module provided to the content-using device; a detection
unit that detects whether or not the content-using device is located
within a distance, from an access point, within which radio signals from
the content-using device reach the access point; and a communication
on/off operation detection unit that detects whether or not a user
operation of turning on/off communication has been received. This enables
the content-using device to immediately notify the content management
server of the online state thereof.

[0768] The content-using device may further comprise: an invalidation
instruction reception unit that receives an invalidation instruction from
the content management server; an invalidation unit that invalidates the
content according to the invalidation instruction; and an invalidation
response transmission unit that generates an invalidation response when
the content has been invalidated and transmits the invalidation response
to the content management server. This enables the content-using device
to immediately invalidate the content according to the invalidation
instruction from the content management server.

[0769] The content-using device may further comprise an invalidation
display unit that displays a record of the invalidation of the content
when the invalidation unit has invalidated the content. This enables a
user of the content-using device to acknowledge information pertaining to
the invalidation of the content.

[0770] The content-using device may further comprise a display unit that
displays how the control of the use of the content is being performed by
the content control unit. This enables a user of the content-using device
to acknowledge the period of validity of the content, etc.

[0771] Another aspect of the present invention is a content distribution
method for use in a content distribution system including: a content
management server that manages a content; and a content-using device that
uses the content, wherein the content management method comprises: a
first online/offline detection step, by the content management server, of
detecting whether the content-using device is online or offline with
respect to the content management server; a device management step, by
the content management server, of managing an online/offline state of the
content-using device; a content management step, by the content
management server, of managing a state of use of the content in the
content-using device; a second online/offline detection step, by the
content-using device, of detecting whether the content-using device is
online or offline with respect to the content management server; and a
content control step, by the content-using device, of managing a period
of validity of the content and controlling the use of the content
according to the detection in the second online/offline control step.

[0772] Another aspect of the present invention is an integrated circuit
that forms a content management server in a content distribution system
including: the content management server, which manages a content; and a
content-using device that uses the content, the integrated circuit
comprising: a first online/offline detection unit that detects whether
the content-using device is online or offline with respect to the content
management server; a device management unit that manages an
online/offline state of the content-using device; and a content
management unit that manages a state of use of the content in the
content-using device.

[0773] Another aspect of the present invention is an integrated circuit
that forms a content-using device in a content distribution system
including: a content management server that manages a content; and the
content-using device, which uses the content, the integrated circuit
comprising: a second online/offline detection unit that detects whether
the content-using device is online or offline with respect to the content
management server; and a content control unit that manages a period of
validity of the content and controls the use of the content according to
the detection in the second online/offline control step.

[0774] (18) Specifically, each of the above-described devices is a
computer system composed of a microprocessor, ROM, RAM, hard disk unit,
display unit, keyboard, mouse, etc. Computer programs are stored on the
RAM or the hard disk unit. Each device achieves its functions by the
microprocessor operating according to the computer programs. In order to
achieve predetermined functions, the computer programs are composed of a
combination of multiple operation codes that indicate instructions for
the computer.

[0775] (19) Part or all of the constituent elements constituting each of
the above-described devices may be assembled as one system LSI (Large
Scale Integration). A system LSI is an ultra-multifunctional LSI produced
by integrating multiple components on one chip and, more specifically, is
a computer system including a microprocessor, ROM, RAM, and the like.
Computer programs are stored on the RAM. The system LSI achieves its
functions by the microprocessor operating according to the computer
programs.

[0776] Further, each of units of the constituent elements constituting
each of the above-described devices may be separately integrated into a
single chip, or may be integrated into a single chip including a part or
all of the such units.

[0777] Further, the method applied for forming integrated circuits is not
limited to the LSI, and the present invention may be realized on a
dedicated circuit or a general purpose processor. For example, the
present invention may be realized on an FPGA (Field Programmable Gate
Array) being an LSI which can be programmed after manufacturing, or a
reconfigurable processor being a LSI, reconfiguration of which could be
made to the connection of internal circuit cells and settings.

[0778] Further in addition, if a new technology of circuit integration
replacing that of the LSI emerges as a result of the progress made in the
field of semiconductor technology or another technology deriving
therefrom, the integration of function blocks may be performed applying
such technology.

[0779] (20) Part or all of the constituent elements constituting each of
the above-described devices may be assembled as an IC card or a single
module that is attachable to and detachable from each device. The IC
card/module is a computer system that includes a microprocessor, ROM,
RAM, etc. The IC card/module may include therein the above-mentioned
ultra-multifunctional LSI. The IC card/module achieves its functions by
the microprocessor operating according to computer programs. The IC
card/module may be tamper resistant.

[0780] (21) The present invention may be each of the above-described
devices or control methods for controlling the above-described systems.
The present invention may be computer programs that achieve the methods
by a computer, or may be a digital signal comprising the computer
programs.

[0781] The present invention may also be a computer-readable recording
medium having recorded thereon the above-mentioned computer programs or
digital signal. Examples of such a recording medium include a flexible
disk, hard disk, CD-ROM, MO, DVD, DVD-ROM, DVD-RAM, BD (Blu-ray Disc),
and semiconductor memory. The present invention may also be the digital
signal recorded on such a recording medium.

[0782] The present invention may also be the computer programs or digital
signal to be transmitted via networks, of which telecommunications
networks, wire/wireless communications networks, and the Internet are
representative, or via data broadcasting.

[0783] The present invention may also be a computer system comprising a
microprocessor and memory, the memory storing the computer programs, and
the microprocessor operating in accordance with the computer programs.

[0784] Also, another independent computer system may implement the
computer programs or digital signal after the computer programs or
digital signal is transferred via being recorded on the recording medium.
Also, in the present invention, another independent computer system may
implement the computer programs or digital signal after the computer
programs or digital signal is transferred via one of the above-mentioned
networks, etc.

[0785] (22) The present invention may be any combination of the above
embodiments and modifications.

INDUSTRIAL APPLICABILITY

[0786] According to the content distribution system pertaining to the
present invention, the management of a content in the content
distribution system is performed according to a method for controlling
the use of the content which is determined according to whether or not
the content-using device is connected with the content management server.
As such, protection of the content, which has been provided by a
provider, is realized while a user utilizing the content is able to use
the content with an enhanced degree of convenience. Due to this, the
present invention is useful as a technology for performing management of
a content distributed via a network.